Ok, sorry im taking the PS3 side for most of this one...
Well, look at the competition and the turnaround times there, probably the biggest game graphics wise for the 360 that is actually supposed to compete with UC2 or KZ2, Alan Wake, has been in development since before the PS3 was released... Outside of that and nifty CG scenes no other games really come close. So I don't think it really has much of anything to do with understanding the cell processor. I'm not sure i'm following the 3 and a half years either... KZ2 was released a year ago, which means the understanding behind how make what im assuming you are implying as mind blowing games came far before that. Realistically from the developer's perspective,at the very most you could probably get off saying a year and a half or less. But even games like Uncharted: Drake's Fortune at the time it was released blew anything else out of the water. The bar has not been getting raised by the 360, sorry folks, it just aint true, its ps3 exclusives that you can thank for all the awesome looking games that are starting to show up, even bungie admits that KZ2 was a wakeup call that they need to step things up and now look how much better halo:reach looks.
I own both consoles, and I have to say that graphics wise pretty much all the 360 games up till recently were about as appealing as dirty butt... who knows some of you may like that i dont know... Now, the 360 is finally stepping up its game with splinter cell : conviction, alan wake(finally), and halo:reach.
Anyway, if we are going to discuss something, lets discuss why the heck the 360 games sucked for so long and are JUST NOW matching what we have been seeing for PS3 exclusives.
Essay Pro