What possible reason would Bethsoft have to lock themselves into an exclusive deal? What benefit is there, to them? They don't need Microsoft's money, and FO3 sold almost the same amount on PS3 as on the 360. Why lock out half of their potential sales?
Microsoft would have to pay them enough money to cover the loss of the PS4 and PC sales. Which, given what I have read about Skyrim's sales numbers, would be an incredibly massive amount of money, which makes me think it's near impossible. We're talking like half-a-billion dollars. I really can't see Microsoft justifying that in any way. Now, just cutting out the PS4 and making it a Microsoft exclusive (Xbox and Windows) would be cheaper, but still a crazy amount of money surely, especially since PS4 has a strong early lead.
I just don't see it happening. I'm sure MS is trying to get a timed exclusive on the DLC like they did last time, or maybe on the game itself, and perhaps that is being exaggerated in these "leaks," if they're leaks at all.