As always it comes down to resources. AMD provides full support at launch time on Linux via the proprietary driver. This is possible, considering the relative sizes of the Windows and Linux desktop market share, due to code sharing. In open source we strive for basic Linux support close to launch time as well as providing information and advice to enable further development in the open source community. Adding new features to 7 year old hardware or tiny fringe OSes, doesn't really bring in new revenue, however, the information we release and the open source driver source can be used by interested developers on smaller platforms to add or augment support.