It seems that the GMA500 is just someone else's product that they rebranded. Hence, they can't provide open drivers because the "intellectual property" is not theirs to "disclose". This doesn't make it acceptable, of course, but it does explain their logic. Laziness, not evilness.

All I know is that xrandr works on the GMA hardware but not on nVidia hardware...

(And to be fair to Intel, they are the only company that are releasing any Linux drivers for WiMax.)