what's wrong with Opengl?
I have nothing against OpenGL, myself (in fact, I like that it's out from under Microsoft's thumb). But in my experience as mentioned above, 65% of users chose DirectX when offered a free choice of any graphics/platform. That's the only reason that I consider DX so important: it seems to be what people are using by a 2:1 margin over OpenGL (whether Windows, OS X, or Linux).