I don't think that MS forced Blizzard to run the game at 1080p. They certainly wouldn't have blocked the game. I don't think he was meaning to be taken literally. It sounds like a good natured conversation and not a developer airing dirty laundry.
I think what MS did is use technical assistance to help them increase performance, and asked them to use 1080p if they possibly could. MS clearly want higher resolutions, but I'm calling bullshit on Blizzard being forced to do it.
That said, my preference would have been for keeping at 60 as often as possible instead of dropping to 50, which they could have managed easily with a smaller resolution increase to, say, '990p'.
Lots of people won't be bothered by these smallish dips, as widely lauded games such as Killzone, Infamous and Titanfall have shown with their far lower and more erratic frame rates, but it's sad to see a developer make the decision at the very last minute to put resolution before their gameplay objectives even if it's only a small tradeoff.