There is A LOT floating around about MGS4's exclusivity.
2005:
http://www.joystiq.com/2005/06/17/no-ps3-no-mgs-soup-for-you/
2006:
http://www.joystiq.com/2006/12/17/heightened-rumor-metal-gear-solid-4-not-a-ps3-exclusive/
Now unless I see Sony handing over a bag of money with a contract that says "Only for PS3, Kojima... Only for PS3" then I don't see what's stopping Hideo from going multi-plat.
FF13 is exclusive to PS3, I believe.. No rumors.
Understanding is the key.







