Quite interesting thoughts.. my two cents,
1. valve has a history with problems in the Half-Life engine, so yeah you could doubt them a bit, but after seeing what they've managed to do with the physics side of HL2 I'm willing to wait and see irregardless of performance. They very well might have decided to avoid new dets for compatibility rather than forcing use of newer, or it could have been they didn't like performance :P
2. yeah nVidia kicks ass.. and yeah it worries me that Andy hasn't been around. One of the best things going for nVidia's support of linux was more than code.. it was support, and I hope to see that continued. Seeing the driver versions change doesn't worry me tho, note that the changes being made to the windows drivers (changelog) aren't huge, and really not too big a deal for the linux end to follow so far.
3. ID engines run openGL better than others because of code. Carmack's theory of design is as simple as it gets, but fast because of it. In contrast, M$ never coded something simple in their lives with all the manpower they have, and of course its slow because of it. Weird eh?