Just a break from my current theme, to point to this piece "DRM, Incompatibility and Market Power: A Visit to the Sausage Factory" by Ed Felten. It is a superb account of the motives and incentives that produce the DRM that we are seeing today. It needs to be listed along with Cory Doctorow's 1994 talk at Microsoft as the essential reading to understand the subject. This is why I insist that the mechanisms (technical and legal) of enforcement of copyright are more significant than the questions of what is copyrightable and what isn't
"Running through this whole convoluted tale are two consistent threads. DRM is used as a weapon not against infringers but against market rivals. And when companies use DRM to undermine compatibility, law-abiding customers lose."