I haven't done a quantitative study, but I've had the impression over the past several months that patents dealing with rights management have been issued at a slower rate than in the past while at the same time there seems to be more patents dealing with watermarking issuing. It may be that those with fundamental patent portfolios relating to rights management such as Intertrust, ContentGuard, and perhaps Macrovision and increasingly Microsoft have pretty much exhausted the most fertile areas and that subsequent inventions will of necessity be much narrower in scope.
A few years ago, a well-respected senior computer scientist opined that the most important work in watermarking had not yet been done. Contrasted with rights management, it may be the case that researchers are finding watermarking a more fruitful area for innovation and patenting.
The US Patent Office issues new patents on Tuesdays. Issued patents and published applications may be early indicators of the kinds of issues being addressed by inventors and/or the companies for whom they work. Assigned to Kaleidescape, Inc., the first patent addresses watermarking and fingerprinting digital content using alternative blocks to embed information. Assigned to Musicrypt, the first of today's patents entails a biometric rights management system.