If the sales of FFXIII are any indication, FFXIII is a pretty big hit on the 360. Not as big as on the PS3, but still pretty big. A large part of this is because MS was able to get SE to develop the game for the 360. They paid them to develop on the 360, they paid them to get advertisements for only the 360 version, and they paid them for a bundle. Now, if SE were to develop for the 360 only in the US, they would lose a lot of money by not developing for the PS3. But if MS has enough money to get all the deals they did for XIII, can't they go a little further and pay SE enough to compensate for the revenue they'd lose by not developing on the PS3? SE would get enough money to make up for the money they lose and MS would have another exclusive, another reason for people to buy the 360.