Via Dave Farber's IP list comes Bob Frankston's excellent essay on "why DRM can be problematic rather than simply annoying." Explains Frankston to the list (emphasis, mine):

The juxtaposition of Microsoft's effort to build the control of content into basic hardware and the comments on the Discovery Institute's Intelligent Design agenda gives insight to the problem -- if you believe you can design the future then why not lock in the incumbent's control?

DRM is a way of assuring that the "content owner" can maintain control. That seems innocuous in itself but it has the effect of limiting the marketplaces' ability to change. This makes sense in limited cases as it allows investors to recoup the cost of their investment and make a profit but if DRM works too well it prevents growth. A marketplace is a dynamic system that keeps changing. Why doesn't the marketplace simply devolve into chaos? The reason is that it is an evolutionary process -- one that provides opportunity for creating new results. We can think of this opportunity in terms of Chris Anderson's long tail -- it represents the value to be discovered rather than what is obvious.