I'm going to say Free online and that most people don't use a headset online.
Where as on 360 almost every at least has one, so there is alot more smack talk going on in the lobby's and in-game.
That doesn't mean the PS3 online community is devoid of idiots though, it seems like most regret buying a headset and have resolved to playing annoying music or making annoying sounds for an entire match.