I'm no audio maven.  I read a lot of posts about the sound quality of the samples in various instruments. For example, I have read post that say that Jamstix and Session Drummer samples lack a certain sound quality found in BFD 2 or other such high end drum samplers. 
 
To be frank, to my composer/arranger only ear, the only difference I can percieve is that the BFD2 samples are louder.  If I turn up Session Drummer to the same level, its hard for me to percieve any deficiency.  Could be just my Rokkit 5 monitors are not able to to show the difference.
 
So, my question is, how do the samples really compare in quality?  Is there enough difference in quality to justify the enormous price difference?  What benefit would one get from BFD 2 sounds that would be lacking in Session Drummer or Jamstix sounds?
 
I would appreciate some clarity from you experienced audio guys...

Assuming all samples are recorded top quality (soft to hard hits) and by just comparing samples, what sets them apart would be how many samples are included.

** Velocity layers :

BFD 2 has up to 96 layers for each note.
Session Drummer 3 libraries from Platinum Samples, up to 16 layers.
Session Drummer 3 default libraries, from 2 (electronic) to 7 (acoustic) - could be more, that I've missed (from looking at the samples directory).

The more layers, the more responsive the sound may be. But also depends, if the midi data had max or fixed velocity, you may not hear much difference.

** Round robin (within the same velocity layer) :

To prevent machine gun effect, many libraries have multiple samples at the same velocity layer, and are cycled during playback.

** Raw / Processed samples

BFD 2 features raw and long samples where you can further customized the sounds or use presets with active processing (filter/eq/comp/etc..) making BFD more flexible.

Session Drummer 3 samples are already processed.

Thanks Albert, that helps me understand better.