It has alot to do with the community as well, say what you will about the Halo community, they believe in their franchise strongly and they treat it like their number one shooter, some in the PS3 community on the other hand tends to second-guess everything constantly and can't seem to rally behind one product, some people also tend play a lot of second-tier shooters that they can't even make up their own mind which shooter to stick to.
Very often I see people recommending a shit-ton of games to other people, there is no focus, most often people don't even have a clear idea which ONE game to recommend to their friends, it's like "oh get warhawk, oh get SOCOM, oh get Killzone 2, oh get COD4...", they can't even name ONE game in each genre to recommend to people, IF this is the game you believe to be the best game on the system, tell your friends to get it, get your friends to play it. Don't tell people to get Killzone 2 and then go "oh you should get MGS4 too, oh you should get warhawk too" when they ask you to recommend to them ONE game to buy.