Microsoft does nothing for free, for which reason do you think that Microsoft is spending money and men-labor making the DRM protection in Vista?
Microsoft sells Windows and not DVDs or CDs, what is the importance of RIAA for Microsoft?, Microsoft can easily release another Windows without any kind of protection and people will buy it, Microsoft doesn't need any RIAA for selling his Windows.
The only reason by which Microsoft is puting DRM into Windows is for making money  from the content creators. If they don't pay Microsoft there's no reason to exist DRM in Windows, Windows will sell with or without DRM, well... a little less with DRM.

Quote - Vista essentially does not do anything to protect the content, per se, only the interfaces that the content must pass through - from the Blu-Ray or HD-DVD disc to the media player to the video and sound cards and finally to the screen and speakers;

All the protection is done by Vista!!!!,  the only reason that the interfaces must have a hardware proteccion is to help Vista. And Vista use CPU time for making the protection!!!!, so your software will run much slower with Vista.
Without the hardware's help Windows protection would be flawed, anyone would be able to install a device driver that access directly the hardware ignoring all the Vista protection.
Never mind, Vista protection would be flawed anyway, you always are able to create a device driver that bypass all the hardware and software protection.
RIAA and Microsoft lives only in a dream world and don't forget the Asiatics that will flood the market with DRM-less computers.

Stupidity also evolves!