So, I really see no reason why ATI should have gone the route they did with the Radeon 9700.
It now is seeming to me like it was more of an engineering cost issue. They wanted to spend time elsewhere instead, feeling that their aniso implementation was, "good enough," and would rather spend time on other things.
I will see if I can find the post from the ATI employee that stated that they thought their AF is fine and just wanted to improve their angle perfromance. I thought I saw it back on B3D from OpenGL guy...Your theory is based off on techincal facts however thats not why ATI chose this method of Aniso (again look at the speed tradeoff this method gives). Also if I remember OpenGL guys this was the same AF that they used in the 8500 just with tweaks (angles and tri-linear).