It's just an API. How exactly is it 'behind'? There's nothing in Direct3d that can't be done with OpenGL. Both Nvidia and AMD contribute to the standard, it's been evolving rather rapidly over the last couple of years.
People use Direct3d on Windows because it's built in, it's heavily promoted... And it makes porting to the xbox very easy.
If OpenGL wasn't capable, then why does John Carmack continue to use it for ID's game engines?
It's not just heavily "promoted". It's heavily "upgraded" as well. Theoretically, you can do any graphics you want on any video card, any CPU, any motherboard, and even without either OpenGL or Direct 3D. It's been done that way for decades. The problem is it will take longer to develop your applications without an API (Applications Programming
Interface...much like how a touch interface makes it easy to use computers), and it will take longer for your real-time processing of graphics to occur for the same exact picture! Without these API's it would cost you much more money to make the same game, as well as if you push the edge, you would not be able to make your game smooth without the API/GPU accelerated content.
Therefore, when Direct X / nVidia includes the latest "interfaces" for "real-time smokey reflections" and whatnot, developers will actually make a game than shows off their art in competition with one another. Even if games like WoW, EVE Online, etc. will never make an XBox version.
And once again, using a "graphics API" is not the hard part of developing the game. XBox/PC portability has more to do with the fact that Microsoft makes both OS's than whatever graphics API they use. As a point in case...OpenGL is usable in many OS's theoretically seamlessly. I'm sure in real-applications there are small querks, but that's about it. It's just an easy to use "plugin" to any of the supported OS's.
I mean if you ever seen how they make games and stuff like on discovery channel etc, it's basically a bunch of calculations flying around, right? So. OK, you don't really need the graphics at all really...if your brain can interpret all the numbers that you see. But since you're not a cyborg...they move on to stick-figures and wireframes made by animators. And then other artists/designers overlay that with a shell made in part by Direct X / OpenGL. Even though is most of what you see, it's really a minute part of the game itself. I mean, nowadays nVidia has the PhysX engine for physics calculations, but that's another story and a different API.
