The thing is, Microsoft is doing what they're good at. They're good at giving a consistent experience across whatever hardware, no matter what, and damn any technical debt or consequences they incur in doing so. I think someone posted a video of them actually running the upgrades from Windows 1.0 through to 7 on youtube somewhere.

Throwing touchscreen devices into the Windows wheelhouse and trying to write one OS that runs across them and desktop machines is actually very much a bet on MS's core competency.