The doctrine of first sale, at least in US law and from my limited not-a-lawyer understanding, says that if you buy something, then you own it, and you may later sell it to a third party without the permission or consent of the copyright owner, the original seller or anyone else. So if I buy a book from a bookshop, then read it, I can later sell that copy at a garage sale at my house, lend it to a friend or give it away to charity, and the bookstore, the publisher and the author don't get any say in the matter, nor any cut of the sale price.
People argue for this right to apply to digital goods as well, such as music purchased from iTunes. A recent court decision, however, says that first sale does not apply to digital goods, only physical ones. There are two possible responses to that decision. One is to cry foul against the court, asserting that digital first sale is a right that should exist, since we are told that we have bought this music (or book or movie) and therefore we have the right to sell it to a third party, provided we do not retain a copy ourselves. The other option, and one that I find quite plausible, is to say that the "sale" of a digital good, if it cannot be resold at all by design or by nature, is nonsense. If I am not "buying" music from iTunes in the sense that I may resell it, then I shouldn't be charged that way for it, and iTunes needs to change to a different fee model. They need either to charge for music "rental", for limited-term access to music that goes away after a while, or for flat-fee unlimited access to the whole library (or by parts, such as decades or genres).
Mokalus of Borg
PS - If you can't resell it, you haven't bought it.
PPS - And if you haven't bought it, you shouldn't be charged as if you have.