AF drop is very bad compared to competition 8800GTX in BOTH parts (R580 also suffered texture hardware deficiency).
In 2 out of 3 games the AF drop HD2900 is much more than X1950, in 1 game it is similar. I dont think that bears out your statement. One tie and two severe losses.
The AA results are troubling though, though the sample size is small.
http://www.tweaktown.com/reviews/1115/1/page_1_introduction/index.html
This newer teaktown review in which for some reason they did not turn on AA/AF is interesting and bears out what we are saying, without AA and AF 2900 performs very well, often beating 8800gtx. And at least placing much closer to 8800GTX than 8800GTS.
The AF hit can be more significant on R600 at this time. It should show higher quality in exchange (not on the LOD isotropy front, but on the mipmap transition front). I believe some of that will be addressed, in part, in future drivers. I can't promise a % improvement at this time.