It is interesting... I was speculating on his current opinion on this matter in another thread if some of you would remember.
As for why he did not mention AMD, it is probably just that he never had the opportunity to try out the free radeon drivers with the hardware he has. It does not really matter, as so much is shared (especially between the radeon and nouveau drivers, as well as Intel to a lesser extent) that if you have a good experince on one, it bodes well for the rest.
Also, nouveau has arguably had the most progress in the past few years as AMD was so much more ahead. For instance, take my rather common onboard GeForce 6150 SE that came with my motherboard and then compare my external Radeon HD 4670. When Fedora 13 was released in 2010, the radeon could play Doom 3 and many other older titles, although it lack S3TC support at the time. Nouveau could not even launch glxgears.
With Fedora 14 in November 2010, nouveau started rendering things, but it could not even get a game like Rune to draw right. Fedora 15 released last May proved to be the one to hit the jackpot for both. radeon switched to Gallium and got S3TC support, and nouveau could finally actually start handling 3D tasks. That is a fairly impressive transition.
If you want to keep on trolling crazycheese, I suggest you ask Gordon first. He is very receptive to inquiry, as long as it is not about UT3.
As for why he would not want to move, he only recently got married and now has a two month older daughter. He has a lot more on his plate now than he used to. I am not surprised if he is happy doing what he is doing now - porting Humble Bundle titles and living in North Carolina. It is time for the next generation of icculus's to emerge.