Peter Fader, a marketing professor in Wharton, was interviewed few months ago about the Radiohead’s release of their album online (Radiohead’s Free-for-all: Performance Art or New Business Model?, registration required).
He got it wrong when comparing movie DVDs to music CDs.
When you view a movie, you want to view it on a big screen with speakers, in a comfortable surrounding, and with popcorn or sunflower seeds on hand. Thus, viewing a movie is not an activity to be performed at any random place and time. You have at most few venues in which you would view a movie. Therefore, it is feasible to force you to use a memento, (such as a VCR cassette or a movie DVD) having a volume and a weight, to view a movie.
On the other hand, music is consumed in iPODs and MP3 players and everywhere. So ideally, you want to have it as a weightless bitstream. Therefore, any attempt to lock music down to a CD album would be counterproductive. Similarly – for books. While books require one’s undivided attention, one wants to read them at idle moments everywhere. Therefore they had better be available as weightless bitstreams in e-book readers, as well.