Licensing is one thing and I don't think any of us know the details of EA's deals other than they commit them to producing a game once a year and they have exclusive rights.
However, the argument that the games are "too big" ignores the reason why this acquisition has the potential to happen. The entire purpose of buying EA would be to beef up their lineup of exclusive titles - they are buying EA for Battlefield, Fifa and Madden. No one is going to buy an Xbox because Peggle is an exclusive title.
Microsoft won't stop to shed a tear about the loss of in game transactions from one platform. The entire point of the buying EA is to drag more gamers across to their platform. As soon as they move away from that the reasoning for buying EA (or any other major studio) doesn't stack up.
TLDR; If EA is purchased the only thing that will stop a title becoming exclusive (in time, maybe not immediately) will be the license. They are only buying EA for exclusives.