Just read this from TheGameReviews site about MGS4 coming to Xbox 360. I guess it was just a rumor but you never can tell nowadays.
http://ps3.thegamereviews.com/story-342-Rumor-Killer-No-MGS4-on-360-says-Konami.html
TheGameReviews.com had the opportunity to speak with Konami’s PR about this latest rumor, and unsurprisingly, Konami is baffled by claims that Metal Gear Solid 4 is going multiplatform. In a rush to get the word out, it seems that those who broke the story talked to everyone except Konami, who made this statement "For the record, Metal Gear Solid 4: Guns of the Patriots is a PlayStation 3 exclusive and there are no plans to develop an Xbox 360 version of the game." Nuff said..