iTunes, DRMs and the first sale docrine (?)

I am wondering if anyone has any thoughts on something I've been thinking about. In class yesterday, Professor Laster, in his summary, said that the first sale doctrine exhausts the copyright holder's right to control the distribution. As I understand it, that means, for example, that if I buy a music CD, I can lend it to my friend. I know Apple recently announced it would stop selling music encumbered by digital rights management restrictions - seems to me as a result of consumer power - but are DRM encumbrances legal? Was apple allowed to do this in the first place? Ostensibly, when I buy a song on iTunes, I'm not just buying a license to use the song, am I? Or maybe I am? I thought I was buying a copy of the song. Does it have to do with a difference in medium, ie the tangible medium problem? Am I missing something? A statute? At any rate, it seems like in this case the market took care of the situation and Apple is now getting rid of its DRMs. Victory.