http://bugs.winehq.org/show_bug.cgi?id=30270
--- Comment #32 from Roderick Colenbrander thunderbird2k@gmail.com 2012-06-26 15:05:10 CDT --- I have added some Wine fixes related to OpenGL extension loading. You will now see a warning message.
In my testing I found Steam to be plain stupid since it really tries to load OpenGL functions before OpenGL is up. On my system using Nouveau Steam starts fine even with Steam doing stupid stuff. Later on Steam initializes GL properly.
I can't say what the real problem is you guys are seeing, but I doubt the GL extension stuff is related.