tobiaslindahl.  I build my own desktops but that is not for everyone.  Same holds true for factory build's (e.g. a Dell).
There are many that want a "plug and play" system and a self built or factory build requires more than "plug and play".  Thus the custom builders come in as they have the expertise to do exactly that and deliver a fully configured specialized "plug and play" system to their customers.  
 
An off the shelf factory built system takes some knowledge to get it set up for use a recording DAW.  Not just "tweaking the OS" but removing factory installed apps that can or potentially can interfere with recording.  A point in that is a Dell laptop that I bought last year for off site recordings.  I worked on the Dell factory disc image install but was not able to fully get it to the point it could reliably record - with my knowledge and help from some Dell engineer friends (at Dell HQ in Round Rock Tx) I still had an occasional drop out (about every 20 minutes) when recording.  I was able to overcome this and get it set up for recording but that took a complete clean install of only the OS, needed drivers and the DAW software and recording interface drivers.  Which brings us back to the point of why many buy the specialized/setup systems from DAW builders, such as Jim Roseberry (with his 25 years of experience with this). 

fireberd
tobiaslindahl.  I build my own desktops but that is not for everyone.  Same holds true for factory build's (e.g. a Dell).
There are many that want a "plug and play" system and a self built or factory build requires more than "plug and play".  Thus the custom builders come in as they have the expertise to do exactly that and deliver a fully configured specialized "plug and play" system to their customers.  
 
An off the shelf factory built system takes some knowledge to get it set up for use a recording DAW.  Not just "tweaking the OS" but removing factory installed apps that can or potentially can interfere with recording.  A point in that is a Dell laptop that I bought last year for off site recordings.  I worked on the Dell factory disc image install but was not able to fully get it to the point it could reliably record - with my knowledge and help from some Dell engineer friends (at Dell HQ in Round Rock Tx) I still had an occasional drop out (about every 20 minutes) when recording.  I was able to overcome this and get it set up for recording but that took a complete clean install of only the OS, needed drivers and the DAW software and recording interface drivers.  Which brings us back to the point of why many buy the specialized/setup systems from DAW builders, such as Jim Roseberry (with his 25 years of experience with this). 

Fair points. I guess my comment was more for those who actually can put together a PC themselves, which I actually believe are quite a few. I fully understand if people do not want to do that though. It takes a bit of work, but if one is careful and take enough time it is not that hard. But still, I see your point.
In a specialized setup are there any special parts that go into it, making them different from "normal" systems in that the parts are not off the shelf stuff? I get they are most likely build for silence ( maybe ) and obviously performance etc, but that can easily be done buying the right parts yourself ... if you fall into that category of people who can, that is. Maybe I just assume people are more comfortable with this kind of stuff than they really are. Could be the case. 

A great DAW is the sum of everything (parts, performance, quiet, tweaks to BIOS/OS, etc).
When you go to a professional of 25 years, there's nothing left to guesswork/happenstance.
All the details have been attended to... 
Speaking for myself, I've built/supported thousands of machines.  
That amounts to many thousands of hours of experience. 
IOW, We don't rely on NewEgg "user-reviews" (often flawed with pilot error/inexperience) or PC part-picker.  
It's no different than a guitar builder, auto-mechanic, contractor, etc.
 
I'll liken it to a Fender style bolt-on neck guitar.
Almost anyone can bolt together a "Parts-Caster".
However, it will not be the equivalent of a Suhr or Anderson... unless you have advanced skills/knowledge/experience.
 
I like PRS guitars... for the exact same reason.
I don't have to upgrade/change anything.
Paul's guitars consistently look/sound amazing, play amazing, and they're easy to maintain.
It's all in the fine details.
 

Jim Roseberry
A great DAW is the sum of everything (parts, performance, quiet, tweaks to BIOS/OS, etc).
When you go to a professional of 25 years, there's nothing left to guesswork/happenstance.
All the details have been attended to... 
Speaking for myself, I've built/supported thousands of machines.  
That amounts to many thousands of hours of experience. 
IOW, We don't rely on NewEgg "user-reviews" (often flawed with pilot error/inexperience) or PC part-picker.  
It's no different than a guitar builder, auto-mechanic, contractor, etc.
 
I'll liken it to a Fender style bolt-on neck guitar.
Almost anyone can bolt together a "Parts-Caster".
However, it will not be the equivalent of a Suhr or Anderson... unless you have advanced skills/knowledge/experience.
 
I like PRS guitars... for the exact same reason.
I don't have to upgrade/change anything.
Paul's guitars consistently look/sound amazing, play amazing, and they're easy to maintain.
It's all in the fine details.
 

Some good points. I would say though, using you analogy with a parts caster and a Suhr for example, most people will do just fine with a well made parts caster. :) Until you reach a certain level you wont even be able to tell the differance between a Squire and a better guitar. Hell, most blind tests on sound tells me a rather cheap squire will match a more expensive amercan made strat for example, unless you know beforehand which is which. Playability might differ somewhat, but usually small mods will fix that too and make them play on par, pretty much. 
It is not going to be top of the line premium, but more than good enough for most people. I realize there are levels to everything, instruments, computers, speakers etc. Been doing this for long enough to know that for most people, getting that last 5% of performance that might come from a PERFECTLY calibrated system/instrument, is not going to be needed or even noticed.  
 
Not trying to knock specialized computers, for pro's who want the absolute best I could see the need more so than for a hobbyist kind of a guy. But what teh hell do I know :) My PC might be dog **** for all I know.

If you pickup a Fender custom-shop guitar... and compare it side-by-side with a Squire, the difference in quality/playability is pretty obvious.
 
Same with a Gibson Les Paul...
Pickup a R9 and play it for a while.
Now, immediately pickup a Les Paul Studio model.
 
In the case of PRS, their stock "Core" models are typically excellent in most every way.
But pickup one of their Private Stock guitars.
Makes you wonder just how much better one can build a guitar.
Everything is done to perfection.
IMO, John Suhr and Tom Anderson have done the same with Fender style guitars.
 
Everyone has to live within some means.
High-end gear isn't practical for everyone or every situation.
 
One of my best friends likes to collect guitars.
He jokes... "I don't have money to buy Custom Shop or PRS guitars."
Ironically, his guitar collection cost a whole lot more than mine.
The difference, I have three... he has around 300.
 
 

300 guitars ?! lol jesus christ ! :) 

Three is a good number of guitars to have, and I sometimes wonder which three it would be.  I have, uh...more than three.  :)   BUT...less than 200.

No, three's not enough.

1. Rosewood guitar
2. Mahogany guitar
3. Travel guitar
4. National-style guitar
5. 12-string
6. Nylon string
7. Campfire beater guitar
8. Bass guitar for those occasions when no others can be found
9. The one your wife gave you that you can't/shouldn't get rid of

... and that's only the acoustics.

Wanting a Suhr Modern Select...
Had a Suhr Modern Pro a while back.
Fits that Super-Strat role well (pickups have umph - but not super high output).
Today's my birthday, so maybe it's a NGD.  May liquidate a couple of things to make it happen.
 
Three to four seems to be the right number for me (all electric).
I'd like to have a nice Taylor acoustic at some point... but I fear it would open a (new) rabbit-hole.  

Enough guitars?  I have 12 including 2 Pedal Steel Guitars, 3 basses, 4 acoustic and 3 electric.
The lead guitar player in our band has over 30 guitars, all American made including a Strat Plus that's his main gigging guitar.  He also has about a dozen Fender tube amps including one blackface Twin and two blackface Pro Reverb's.