I would expect MS to do something to get some exclusive content. If you look back to the XBox360 launch, Bioware and Mistwalker were studios that helped to round out the games lineup with some rpg/adventure titles. Those studios are no longer XBox exclusives. If Gears of War goes multiplat, there is little left besides Halo, Forza and Fable (which isn't at its high point). Getting an exclusive agreement for Bioware's next game could fit well with XBox's existing fan base.
However, as has been said already, expecting EA to go XBox exclusive is a bit much. Especially the sports games. FIFA, the NFL, they demand their brand reach as many customers as possible. Titles like Battlefield, too, don't make sense. MS would really have to pay EA all of the revenue it would have gotten from other versions. It really would make more sense for MS to look into buying EA.
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