The DRM Wars
A series of posts by Ed Felton regarding the changing arguments for and against DRM.
First, they argue that DRM enables price discrimination  business models that charge different customers different prices for a product  and that price discrimination benefits society, at least sometimes. Second, they argue that DRM helps platform developers lock in their customers, as Apple has done with its iPod/iTunes products, and that lock-in increases the incentive to develop platforms.
And as evidence of this, there’s an interview with a Universal Pictures spokeman about HD-DVD and Blu-Ray that mentions DRM.
DRMs enable business models, they don't stop piracy. And we want to make sure that we have a rich one without making it so easy so that you can violate what we agreed on when you purchased a movie.