Both of what you write have nothing to do with what i wrote. DirectX 10 might not have been available on XP, but DirectX 9 was, as was OpenGL that exposed the DX10 level functionality through extensions. If anything, DX10 pretty much failed to gain traction exactly because it was not available on the OS gamers wanted to use at the time. Very very few engines used DX10 and pretty much every engine skipped form DX9 to DX11.

Also as i already wrote above, currently there isn't really much of an incentive for people to switch (outside of ideological and/or very niche reasons) so the "Desktop Linux dream" doesn't apply.