Development for the PS2 (or Gamecube...) is a different matter than home computers (which this thread is primarily about). If you want to get into that issue, you could go ahead and toss in cell phones, PDAs and a dozen or so other electronic devices.

When you get to that point though you are no longer dealing with OpenGL or DirectX. There is a lot of hardcoded routines in the consoles - as well as proprietary libraries to run on proprietary hardware - with proprietary interfaces. The Playstation itself does not use OpenGL (at least not the PS One or PS2). Gamecube (as I have had it explained) also does not use OpenGL. None of the current mobiles are using OpenGL - although a few have looked into options like OpenGL ES.

So, I would still be willing to say that DirectX is the most common interface since it is used in PC games and the XBox consoles. The only thing that might come close would be Sony's proprietary interface...but I don't think that will quite do it.