Since no one has mentioned it, this rumor has been thoroughly debunked.
Originally Posted by Rakeesh
How so? Even Carmack himself said the opposite, even said DX is far better in his opinion, but that he uses OGL instead as a matter of principle.
He didn't say it was far
better, it just handles some things better. DirectX being the better API doesn't quite equate to it being more flexible in all things. Rage, for example, is an OpenGL 4.2 game with DX10 level hardware being the bare minimum requirement. Using OpenGL makes it able to run on Windows XP whereas it would be limited to Vista/Win7 systems if it were using DirectX. The ability to use extensions can go a long way.
DirectX also isn't without its own overheads. Their only reason to make the switch would probably be to avoid AMD's shoddy OpenGL driver.