The other thing is that I want to use OS X for everything else -- I much prefer using it for development above Windows, so while you may be correct in terms of sheer dollar value comparison, in terms of opportunity and switching costs it's quite higher than that for me personally.
I'd buy the next version in a heartbeat if they offered it.
What version? There is DX9 support on Linux and IIRC a partial DX10/11 implementation bit-rotting somewhere.
I have to say I managed to have it working and I got a 50% increase in FPS in Steam/Source games running under Wine.
There's the "old" DirectX -> OpenGL translation layer in Wine but it is not really efficient or performant, although it may be enough for GUI applications.
Sadly Gallium3D isn't "Linux" yet. It's only really usable on AMD open source drivers that is very small portion of market and I would say it's 15% at best, but in reality likely 5-10%.