I think OpenGL 4.0 is too new to be implented into RAGE, it was released just 2.5 weeks ago. I mean, new things will always appear and if they keep adding things forever, well, then there's another Duke Nukem Forever

The roadmap and design document for developing RAGE was done long ago, and I imagine they follow that plan rather strictly instead of adding whatever new things that appear during the development.
Still, this is just me speculating as I have no insight of the RAGE development at all, so it's very possible I'm wrong