Maybe, while waiting for more comprehensive solutions to the problem, the viable solution we should all push towards is "social DRM".
Let Amazon (and the other media vendors) embed the identity of the buyer in each file as deeply as they can; and let them sue whoever illegally distributes the files they purchased. But the files must be freely copiable and transferrable among devices (and people, such as within a household or between friends). Just like real books or CDs.
In this way people will have the responsibility to look after their own purchases (so that they are not distributed): in fact any unauthorized distribution via P2P will cause problems to the owner of the file, not to the distributor. But people will finally get to own a piece of media, not a license to access a piece of media that is owned by someone else.
I strongly suspect that the main reason why social DRM is not much used is that the limitations associated to conventional DRM are a bug for consumers, but a (valuable) feature for media vendors...