The GeForce3 in Quake III, high quality textures

The GeForce3 in Quake III, medium quality textures

The GeForce3 in Quake III, low quality textures

The GeForce3 in Quake III, lowest quality textures

Conclusions
As you can see, mip mapping is usually affected by texture quality settings, but only a little bit. ATI's hyper-aggressive "optimization" of mip maps goes well beyond that. Also, quake3.exe shows more aggressive mip mapping than quaff3.exe with at least three of Quake III's four texture quality settings: high, medium, and low.

(It's also worth noting that the Radeon 8500's mip maps are are bounded by two lines that intersect at the middle of the screen. The GeForce3's mip map boundaries come in a smooth arc determined by their distance from the user's point of view. But I'm getting ahead of myself.)

I find it very difficult to believe that what ATI was doing here wasn't 100% intentional. Judge for yourself, but personally, I find the evidence mighty compelling.