I remember those anxious days before Longhorn's release. MS was making a lot of weird threats back then. All the "trusted computing" stuff, as well as the thinly veiled attempts at killing OpenGL on Windows. Despite my above waxing nostalgic about the API, I haven't built anything with D3D in years, for precisely the issues you mentioned. API design quality and performance are important, but they are far from the only factors that go into making such a decision.
My favorite is how I was able to guess from Intel's claims that the 915 chipset can't support WDDM because it don't have a "hardware scheduler" that it is probably referring to the "lost devices" in old DirectX that many programmers likely remember.
