According to a statement by AMD/ATI:
We've always supported open source, and for relevant markets such as servers, we release open source drivers so that companies such as Red Hat can include them in their distros. [...] However, for other markets, such as workstation and consumer, performance and feature differentiation are key metrics. Proprietary, patented optimizations are part of the value we provide to our customers and we have no plans to release these drivers to open source. [...] In addition, multimedia elements such as content protection must not, by their very nature, be allowed to go open source.
This makes one wonder. AMD has also, like Intel, always publicized their specifications and programming manuals for their processors and chipsets.
In related news Intel asked to be able to serve a subpoena (a legal writ which calls you to attend and function as a witness in a judicial proceeding under a penalty in case of disobedience) on ATI in the anti-trust case versus AMD.