The biggest difference between Windows 10’s release and all previous versions of Windows is that Microsoft is going to hand users a new version of Direct X that can deliver significant performance improvements charging them for it.
Xbox 360 not updating video library
We saw a single, canned demonstration from Futuremark that looks as though it was lifted from the same DX12 example code we saw running at GDC last year.
Microsoft predicts performance gains of up to 50% in certain titles, which is in the range of what AMD also predicted (and sometimes delivered) with Mantle.
Microsoft, in contrast, has opened streaming options to of potential systems in the US alone.
Even now, with tablet and smartphone adoption surging, the majority of US households own at least one PC, and the majority of those PCs are capable of running Windows 10.
Whether this type of feature will provoke another temper tantrum and/or multi-year OS development from Gaben remains to be seen, but it wouldn’t surprise me if Valve was less-than thrilled about Microsoft’s continued encroachment into what it undoubtedly sees as its own turf.