you have to consider that Linux is a very small portion of the installed base of operating systems... a very large majority (90%+) of their customers are Windows users and therefore they focus a good deal of their development time on Windows drivers... this is just a fact of life
AMD announced recently that they're going to open source their display drivers. It'll take some time, but eventually you'll get your support. Read this here:http://enterpriselinuxlog.blogs.techtarget.com/2007/05/09/amd-will-deliver-open-graphics-drivers/
