I don't buy the paper = DRM argument (and no, not just because paper is not digital). Paper books being unable to be shared with all your friends is an INHERENT limitation of the medium. Nobody "crippled" paper to tone down its ability to be shared to an extent considered "sensible and sustainable;" it's just what you get when you buy physical objects. However, in a networked world (whether that network be the internet or
sneakernet), digital copies of works have the inherent property of being copyable and distributable to a circle of friends for an infinitesimal cost. DRM is designed to cripple this ability, not content with merely reducing the functions of e-books to that of their dead-tree cousins, often goes further and eviscerates whatever other functions the providing company believes it will be able to get away with while still getting a high number of people to buy their books, in the name of maximizing profit.