OpenGL seems like a no-brainer for future survival as MSFT platform dominance exhibits entropy.
The PS3 used a proprietary API based on OpenGL 1.0.
http://www.eurogamer.net/articles/digitalfoundry-how-the-cre...
What game developer say to themselves,
It looks like in 10 years, Linux and OSX adoption will _probably_ approach 50% market share. Therefore, the best choice for my new game, which will be released in 3-4 years, is to choose OpenGL
I'm not a game developer, but I would bet they are interested in where the market will be in the medium term, and there is no indication Linux/OS X will suddenly dominate within that timeframe.
On traditional PCs and Macs, Microsoft
still owns an overwhelming market share,
with 91.8 percent of all traffic coming
from Windows-based machines. Among non-
Microsoft operating systems, both OS X
and Linux have stalled since October
2011, hovering around 6.9 percent and
1.2 percent, respectively.
Not all of them unless you count using an OpenGL-to-DirectX wrapper library. "Cross platform" sometimes means writing all the platform specific code yourself.
Edit: I guess the point I'm making is, OpenGL runs on non-MS as well as MS platforms (perfectly/badly is another question), but DirectX is locked to Microsoft only. That is what makes it of little to no value for people like me who need to care about cross-platform products and support.