Quote: "Ok you're right , dx9 games probably can run in wine but you still have an *.exe and dll's and dx9 which are Windows specific things.Developing multiplatform games/engines requires lot more than that. Implementation of separate modules for (native) input , rendering , sound etc for all target Platforms (Window-Directx , linux-OGL , Android-OGL-ES etc...)"
No one is disputing this.
Quote: "So while your game runs in wine , you can't really say that your game is crossplatform."
Semantics. If my game has the ability to run on other OSes, that's all that matters.
The point of all this is, that if this was OpenGL, then this would not be an issue to need an extra layer to run the games. It would be a direct API that ALL OSes run. DirectX 9.0c is old school, and newer DirectX versions only run on Windows. OpenGL is the better choice.