newbie needs help with loop samples

I vote for the rex format, but wavs are good too I believe. Here is good thread about this matter I think:
http://forum.cakewalk.com...aspx?m=3116417&p=1

with anything other than rex or acid loops it's quite easy to throw them in the timeline right-click them and select "Groov Clip Looping" wich 99% of the time turns that loop into a rex loop! ENJOY!

Is there a rank below "newbie"?  The acid thing is something I have wanted to understand, but I haven't put the time into it.  As I understand it, ACIDized loops should respond to metronome and also to pitch markers.  Today I have been playing with the new Braintree features.  In particular, I spent a little time with the Hardgroove bass loops.  The WAV loops do indeed respond to pitch markers, so I can see how they could be useful in a composition that has more than one chord.
 
That got me curious about all the other loops that were already available.  I haven't found ANY audio grooves that respond to pitch markers.  The MIDI grooves do, of course.  I understand that the percussion loops can be useful without pitch changes.  But I don't see how any of the tonal grooves (guitar, piano, bass, whatever) could be of any use whatsoever if they don't respond to pitch markers.
 
I feel like I must be missing something important.  Why would people put in the effort of making so many of those loops if you can't shift keys short of running them through Melodyne?  Are there some grooves out there that do respond to pitch markers and I just overlooked them?