Which is another exceptionally good point to have a grievance. It is not a paid exclusive, it is a paid exclusion. Exclusive would mean no PC release either. They paid to not release it on another specific platform. It's a very sordid deal and not one I think paints either EA or MS in very good light.
Not really. And not in the eyes of Microsoft.
Xbox and PC are both Microsoft platforms. It's why games like Titanfall were on Xbox and PC.
By the end of this year both PC and Xbox One will be running Windows 10. Both PC and Xbox will be also be running DX12.
PS4 will not.
That's a huge amount of common ground for multiplatform developers. I think it would be naive not to expect that many developers will place a lot more focus on thinking of PC and Xbox as being part of the same platform, but with PC having more power to play with, obviously. 
That's certainly the picture which Microsoft are painting themselves. Xbox, Windows Mobile, Surface Tablets and Desktop PCs - all running Windows 10 and interacting with each other.
Microsoft see Xbox as their platform for the Living Room and PC as their platform for the backroom/bedroom. I would imagine that this change in direction from Microsoft, of late, may explain why the DLC is also out on PC.