This is really less useful of an example than say, medical records. With AD RMS I can ensure every document floating through an organization is protected with R

This is really less useful of an example than say, medical records. With AD RMS I can ensure every document floating through an organization is protected with RMS, allowing only users with the proper permission access to the document. If someone tries to be sneaky and exfiltrate PHI out of the network it is useless, since nobody outside of the organization can open the file even if they have it. I can also revoke access to specific individuals or groups of people, so even if they had access at one point they can't use it any more. DRM for documents is more about preventing sensitive data from escaping than it is securing communications between parties. The analog loophole always exists, mind you, so it still only makes life more difficult - but it does prevent mass transmission to a large extent.