I can't comment on the file format issue in Office, as I'm not familiar with that.
As far as DirectX goes, I do recall how they released DX 10 on newer platforms (Vista and up). Personally, I think it was a stupid decision, because it limited the potential adoption of DX10 rather than providing an incentive to upgrade to Vista as they hoped. They're pulling the same boneheaded decision to limit the latest DX release to the Windows 8.1, if I recall correctly. Again, trying to shore up a crappy OS release using DirectX will do nothing but cause DirectX to stagnate. The OS's will be replaced in their own sweet time. This seems to be a more recent trend of Microsoft's, and it's a bad one.
I think that the examples you cite are bad decisions on Microsoft's part, not because of what they did, but because they simply did it too soon. I think it's reasonable for them to stop developing software and platform updates for their older software at some point, but with DirectX 10 it sort of had a backlash effect. Even today, overall DX11 use is often paired with a DX9 compatible rendering engine simply for legacy WinXP support, even though any modern video card has long had DX11 support in silicon. We're only now seeing a trickle of DX11-only games starting to come out, all because of that decision. Well, that and the fact that the Xbox 360 was roughly a DX9-equivalent machine.
So yeah, some good examples there. I was thinking mostly in terms of 3rd party application compatibility, for which they have a really good record (i.e. you can pretty much play any DirectX videogame ever as long as it was properly written, which I think is pretty amazing). But they've done some fairly silly things with releasing their own software and platform updates.