Erich Schubert writes that
Oh, and I actually doubt that ATI would give away much secrets if it would allow distributing the existing opensource X drivers. It's not as if the specs of their CPU would be a huge surprise to Nvidia. Some actually say nvidia builds the better graphics cards. And Intel does even give away source code. We're not talking about chip design here, or driver optimizations. Just the plain registers and ports.
-- note: what follows is just my opinion and I'm wrong on a regular basis, so take it with a grain of salt --
The problem here is you aren't thinking like a corporation. As far as I can figure, the corporate view here is that you have two options:
(a) Keep the secrets you have. This is the status quo, you know how to make money here, and no-one else can benefit from your secrets even if you yourself can't.
(b) Give away your secrets. This always carries a risk that someone else will find a more clever (=profitable) way to use your secrets than you; thus, companies try to avoid this unless they absolutely have to.
I personally agree that the risk to ATI appears small. However, just to throw out a hypothetical, giving away their register specs would allow other companies to build cards that are register-compatible with ATI's. (Remember the ne2000?) Obviously this would be good for you and me -- but it's almost certain to drive down ATI's profits at least a little by providing more direct competition in the market for graphics cards; thus it's not good for ATI. This may be a far-fetched or overblown concern, but ATI will need a reason to "go uphill" against it when their current strategy seems to be doing just fine.
Intel, on the other hand, is in a different situation; as far as I know, they generally are playing catchup in the graphics area to NVIDIA and ATI, and as a result, they have more to gain and less to lose by opening their specs. [UPDATE] And as I mentioned in my previous post on this topic, the types of cards Intel sells are probably more interesting to free software users than the cards ATI sells. (I'm sorry you don't have any Intel cards -- they seem to have come automatically with most of the new computers I've seen lately, so I assumed it was a trend!)