The Xbox brand was built on Halo's back, and then expanded by the Gears franchise. Of course the shooter fans are going there.
It's so much more comfortable playing shooters on the 360 controller, add in Live to Halo and Gears as exclusives, and you have shooterbox.
But they have done a really nice job of expanding beyond that. Just beyond that top 10 is a whole mess of quality successes in other genres.
EDIT: I just looked at my gamercard below and saw a good illustration - last 5 games, all of which I love: Halo 3, Fable II, Worms, Lips, and Fallout 3. Pretty diverse.







