Quote - M$ has already decided DX10 will be Vista-only.  At moment not much difference between DX9 and DX10 for most games, but it's an indicator...

Something like this happened in the past with video card fabricants.
DirectX is propietary to Microsoft and its use by the video card fabricant must be licensed and cannot be used with something that is not Microsoft.
There's another alternative to DirectX that is OpenGL. OpenGL is an open and free specification from Sillicon Graphics with full available support and tutorials.
Some video fabricants that entered in partnership with Microsoft wrote only  drivers for DirectX without giving any support or releasing any specification for something that was not Microsoft.
Other fabricants instead wrote drivers for DirectX and OpenGL and gave support for Linux, the result was obvious, tell me who will purchase today a video board that hasn't OpenGL?
Even Poser and DazStudio are based on OpenGL and not on DirectX.
Something similar happened with SoundBlaster. Many years ago SoundBlaster was the most popular audio card used by almost all computers and if a card was not SoundBlaster it was SoundBlaster compatible.
One day Sound Blaster become a partner of Microsoft and so, only relesead drivers for Windows and never released any information or documentation for people be able to write drivers for other systems.
What happened?,  tell me today how many computers have a Sound Blaster card?, most of the cards or on board chips are Asiatic!!! Result, who was king lost the kingdom and Sound Blaster lost the market.
If Microsoft decides that DirectX10 will be only for Vista it will mean the end of DirectX that will be replaced by game makers by OpenGL, and for games don't forget Playstation 3........

Stupidity also evolves!