When TK first enabled RWRs in SFP1 (in the first patch), they did not work on Radeon cards, and RADAR displays were also hosed. However, they worked fine on Geforce 3s and 4s. Go through the archives on the Thirdwire and SimHQ sites and you'll find quite a few posts detailing this.
With the '06 and '08 patch, shader-driven effects (terrain and water) appeared as "blocky" artifacts on my x800xt. When I switched back to an nVidia-based adapter, those artifacts were suddenly gone. And, I am not the only user to have experienced this, Dave also did, and I'm sure that his response to your argument would probably include a few choice scatalogical terms.
And even today, some users (all of them using Radeons) are reporting stuttering when accessing the avionics60.dll. I have no such issues with my four year-old tech GTX 250, and neither does Wrench with his GTS 240.