Before the exclusivity deal, the game would have been released on Xbox anyway. That's why there is no actual benefit.
A lot of people are saying that this doesn't make the Xbox better for current owners, and only detracts from PS4 and PC players. However, I think the point of this is actually to make the console more enticing to people who haven't bought in to anything yet. That at least makes way more sense to me than the whole "this doesn't benefit me even though I own an Xbox" mentality.
Well of course it is. MS would be nuts to fund this (or very, very desperate) if the only goal was to try and slow up PS4 a bit.
The issue in my view, above all the low level discussion, is that on the evidence the reveal and strategy has gone badly do far.
I doubt Spencer expected to be grilled like the bad guy and end up forced to stick to "no further comment than our initial comment" like he was the bad guy mouthpiece for a huge corp.
I doubt CD or SE thought they'd get quite the mess they have in their forums or twitter feeds.
So far as I can see outside the Xbox fans MS are being painted as the bad guy, the media and social media is negative and in general MS are back as the big evil corp using money and dirty tactics.
That's hardly going to bring people over and to be honest after all the horror of the launch the last thing Spencer needs is this kind of PR.
Add to that general view on Sony post show is lots of new games and lots of fair exclusives.
Market perception is what's killing Xbox right now and helping Sony and this deal seems to have ended up playing right to the established narrative which is not a win for MS particularly in Europe.