Why does the Xbox 360 have trouble with anti-aliasing?

[darkely]

Today I got bored and I fired up my Xbox to play GTA 4 (aka GTA IV (TBOGT) I don't know about others on the forum but my desktop is decent (can play most modern game maxed out) but GTA 4 schools my poor GT430 :'( Any way let me get back on topic... why does the 360 have so much trouble with it? I mean it makes fun games (like GTA and COD (yep I play it)) look bad. I also have other minor issues with it like when too many cops/bad guys try to kill me and I start to shoot things get a bit laggy. Is the game at fault or the system? I have wondered if the 360 is just getting older (well more older) or what...

Note: please don't bash me for playing 360 I don't have that much extra money to upgrade my GPU and what not. As you can probably tell by now I have more than one question... No flame wars please.

EDIT: I also wanted to know when you play a game (lets say GTA 4) when you move the camera while the car is moving does that make the GPU work harder? sorry if these are dumb questions but I don't know the technical side of the Xbox 360 very well.