If it comes out six months after the 360 version, I dont think it matters.
I haven't seen any proof of that though.
It's weird though, as EA is normally a strictly multiplatform developer. Seems like many publishers bend the rules because they like 360 better, same reason it seems many Japanese devs still give the 360 exclusives despite it's Japan sales not justifying it at all.
Microsoft's strategy seems to be to own less developers and contract out more. Keep that in mind. If it wasn't for Splinter Cell Conviction and Mass Effect 2, MS spring exclusives would be looking weak. So I suspect you cant really look at these normally, these are more like Microsoft exclusives not developed by Microsoft, and therefore they cannot go multiplatform. If that's the case Microsoft is probably paying for a lot of marketing for these titles in exchange for exclusivity. I noticed ME2 commercials on the NFL championship games, very expensive ads there.