kruis
Exposing the sinister cartel of retailers who allow companies to pay for advertising space.
It's hard to stand out when all of the games are outstanding.
Seriously though. There are a lot of impressive 360 games out there. PGR4, RDR, Crysis 2 and Gears to name a few.
The actual answer is that devs are forbidden from accessing the 360 hardware directly and the general lack of true 360 exclusives. Almost every game released on the 360 is a multiplatform game (or else a late port from an earlier PC version). Multiplatform games can look extreme good on the 360 (Crysis 2 for instance), but they'll never be a in graphical class all by themselves compared to other games on the same platform.
I have not played Gears 3 but does anybody think the game is graphically superior to everything else on the 360 like for instance God of War was on the PS2? Is there a 360 game from the past two years that raised the bar for 360 console graphics to unmatched heights? Without a dedicated team of seasoned 360 devs coding close to the metal that won't happen. That's not a bad thing, the overall quality of modern 360 games is high, but it also means gamers won't get wowed this late in the 360's game.