Getting back to the original point, regular books have long been allowed to be resold without compensation under the first sale doctrine:
http://en.wikipedia.org/wiki/First-sale_doctrine
This is codified law and settled in the courts. However, many argue that the First Sale Doctrine should apply to ebooks as well. Software went the "licensing" route to get around this doctrine, with some success and some not. AFAIK, no one has tested this law with ebooks.