Since the only operating system which provides Direct X is Microsoft on Windows and some variant of it onthe Xbox. Open GL is the only choice on most hardware or in other operating systems Linux , UNIX , And Mac , and others (like PS3 or nintendo Wii) , on the windows platform it's the traditional API for CAD systems and also many games and fully supported by microsoft windows as well.
After many years of parallel existance the 2 API's (GL and DX) have borrowed and shared many features (well DX did the most borrowing since it came later to the game). Supporting the new graphics hardware, ATI and Nvidia have been the cause of most of the changes - more flexible hardware than ever now, the API's need to change to get full use from it.
If you want the widest possible support open GL is the only API which works across many platforms including windows.
PS3 number 1 fan
