Just to mention MGS again, is it not likely that MGS4 will be ported to xbox 360 some time after the PS3 release?
It's neither been denied or confirmed by Konami but there was a rumour flying aorund back in May, and logicaly it would make sense from a business perspective.
The market is fierce at the moment and the only way Konami won't release it on the 360 is with a Sony money hat and I'm not sure they have the cash to space.
I'd imagine as Hideo Kojima is as big a Sony fanboy as they get and has refused to be involved Konami will outsource it for release maybe 6 months / 1 year after the PS3 release.
MS get the 3rd party exclusives (Mass Effect, Dead Rising, Lost Odyssey, Ninja Gaiden 2, GTAIV chapters, Gears 2, PGR4) by publishing them and thereby taking the money hit from having them released on other platforms.