i think i get what your asking as its something i've pondered myself mainly based on things ive noticed in other trainees, much like yourself.
The guys i know that go proper heavy with low reps seems to develop a more dense look to them. There muscle looks more permanent and less "pumped." As you said it looks like if they stopped training the muscle would stick with them. There growth seems slightly lower than the high rep guys but as i said more permanent.
The guys that only do high rep stuff with lighter weight going for the pump seems to get a more pumped look - their muscle looks kinda inflated and as if it will diminish/atrophy quickly if they stop training.
I have no idea about the science etc... but its just something ive observed.
i tried to find examples to explain what i ment:
Powerlifter who looks thick/dense as hell.
Arnie who sports the more pumped look (imo):
I could, and probably am talking absolute rubbish here!
EDIT: another good example of the dense thing i was on about would be Dorian who went very heavy i believe and had a really grainy stone like look to him blah blah blah..... i really am rambling crap here.
<message edited by BARBUDA on 16 July 2008 00:42>