R300 support isn't just complete.
"ArtX paved the way for the development of ATI's R300 graphics processor (Radeon 9700) released in 2002 which formed the basis of ATI's consumer and professional products for three years afterward."
Dolphin, a completely separate emulation project, can run damn near %90 of all gamecube games. The flipper chipset is nearly the same as the R300.
Of all the graphics chipsets there are open source drivers for, r300 is the closest to matching quality with the proprietary drivers. All of this, with no cease and desist letters? Support from people that *just happen* to know what they're doing? AMD hasn't dropped support for sht. They just don't want your phone calls.