Oh come on. In the end buying exclusivity only helps fanboys. Less people can play it, S-E makes less money and people who would like the game cannot play it.
So I am sure MS paid a lot of money for the simultaneous release but it will be far less than SONY would have had to pay for exclusivity. Because that's wasted money.
I couldn't care less about FFXIII becoming multiplatform, now Portal Alive being 360 exclusive THAT HURTS.