Its a way to keep all commercial game developers targetting Windows and the Xbox 360 while making it much harder to port them onto other platforms and game consoles.
People may see it that way, but back when Alex St. John (now at WildTangent) help create it, they designed it by asking developers what tools they needed and building from there.
Back then, developers wanted 4 things:
1. a supportable way to do graphics quickly without knowing anything about the specific video hardware in the system.
2. Some way to use network services without being networking experts
3. Some way to access joystks and other controllers without know what brand/model is going to be used.
4. an easy way to produce the best quality sound the hardware can support with out knowing that much about the hardware.
OpenGL has never tried to do anything but #1. That is at least one reason DirectX exists.