You have to understand that if Windows had a much smaller market share, say 50%, they wouldnt be capable of leveraging Windows against the graphics companies in that way. They'd lose the ability to compete against other OS's with customers that purchase AMD products. Being that they have the vast majority of the market share they can use that market advantage against other industries --EXACTLY-- the way you just described.
Thats called a monopoly.
In monopoly cases you have to argu superiority. MS can claim, that they have a better product due to the restrictions they've placed on Windows. They can say that as long as you meet the restrictions, you can play back restrictied content at full speed an quality and it will provide a superior experience. AMD would have to argue that there products (minus the restrictions) would provide a superior experience.
I think the only way AMD can effectively argue superiority is to embrace the open source community and help us to work around these DRM restrictions openly. Once AMD has the abilty to play back restricted content without implementing DRM, at full speed and quality, they could easily win that arguemnt.
It's just a matter of whether or not they have the balls to stand up and fight against there oppressors.