Well, one proof that comes to my mind is that Fighting games like Tekken and Street Fighter sell beter on PS3 despite the smaller userbase. So the market for beat'em ups is definitely larger on PS3.
updated: 14.01.2012
playing right now: Xenoblade Chronicles
Hype-o-meter, from least to most hyped: the Last Story, Twisted Metal, Mass Effect 3, Final Fantasy XIII-2, Final Fantasy Versus XIII, Playstation ViTA
bet with Mordred11 that Rage will look better on Xbox 360.