I suppose group can have a pretty strong effect on system. It seems that most DM's/GM's are pretty willing to have a go at different systems, particularly if they want to try their hand at a different genre.
People who only play, OTOH, seem to get fixated on one system to the exclusion of anything else. Not all players of course. Just enough players (as in pure player, no GMing at all) that more or less guide the group into sticking with one (or a small number of) system. I've seen the following conversation more than a few times:
GM: Hey, guys, I got this great idea for ((insert idea here))!
Player 1: Umm, ok.
Player 2: Huh? Whut? Sorry I was checking my email. Oh, new thing? Sure.
Player 3: Oh, really? I hate that sort of thing. I don't wanna play.
GM: C'mon, it'll be fun.
Player 3: No. I tried it once back in band camp and it sucked.
Players 1 and 2: Well if P3 doesn't want to, maybe we should stick with ((same old game)).
Player 1: Oh, and I just got that new book. I'd love to try it out...
GM: ((Sigh))
