Ark of the Covenant from Indiana Jones 1 on the shelf behind him. So the deal with LucasFilm was probably already made in September, around the same time that MS announced they were acquiring Bethesda. Makes me less certain that Bethesda will have told LucasFilm about the MS acquisition talks, which means that Bethesda may have signed a contract that included Sony platforms.
Damn, that really sucks, this would have made a great exclusive counter to Sony's rumored upcoming Uncharted from Sony San Diego and San Mateo studios. But if it's multiplat it doesn't really counter it.
I would assume the MS-Bethesda's negotiations had been undergoing for months before the announcement.
Besides, if MS really wanted to make it exclusive I think it would just be a matter of renegotiating the contracts (a.k.a paying more money) for it. I seriously doubt that all the exclusivity deals that we see pop up every day are signed before the development of said games begin (FFVII, Harry Potter, Kena, CrossFireX, STALKER, Scorn, etc).
On a side note, I thought "hmm, there is something going here," the minute I saw this tweet yesterday: