DRM, Fair Use, and Technical Advancement
DRM has some interesting legal aspects. In many countries, including the USA, copyright includes the principle of fair use. Wholesale copying of a copyrighted work is not permitted without the owner’s consent, but limited quoting is allowed. DRM can prevent this.
Inserting a clip from a song into a documentary about music, for example, would usually be considered fair use. If that music had been purchased from iTMS, using a clip would be impossible, because even Apple’s own Final Cut Express refuses to import the DRM’d music.
Another example comes from the doctrine of first sale. This means that if you have purchased a license to a copyrighted work, you have the right to sell that license to someone else. In the case of iTMS and other DRM-encumbered music systems, this is impossible.
Because many DRM’d works cannot be resold, their resale value is effectively zero. If you buy a CD, and later decide you don’t like the artist, you can sell (or give) it to someone who does. If you buy a DRM-encumbered version of the same album, however, you can resell it only if the original vendor (or DRM author) decides to allow resale.
Another side effect of this restriction is that you cannot use the content in any way not originally envisioned by the DRM author. Imagine the hypothetical situation in which audio CDs had had working DRM. The original intended use of a CD was putting it into a CD player and listening to the recording. Later, CD-ROM drives appeared in computers. These drives would have allowed people to output CD audio to their speakers, but not to extract the digital data from the CD. The line-out port would only have worked if connected to a "trusted" speaker system, so it wouldn’t have been possible to record the audio by connecting the line-out to the line-in on the sound card.
Because the music never made it to the computer, the widespread adoption of MP3 would never have taken place. People would not have started storing their music collections on their computers, because they wouldn’t have been able to do so. Eventually, someone might have come up with the idea of a portable music player. In order for this new gadget to work, it would have had to gain the blessing of the recording industry; otherwise, the equipment would not have been able to copy the music from CDs.
It’s worth noting that content creators rarely drive technical innovation. Historically, the phonographic and film industries have fought to try to ban the player piano, radio, audiocassette recorders, video recorders, and online music distribution. It seems unlikely that our hypothetical portable music player inventor would have received the consent he needed.