B. Mann Consulting

If Apple really wants to boost AAC, it would allow other device and software makers to license Apple's own FairPlay digital-rights-management (DRM) system. DRM is computer code bound to each downloaded track or album that carries instructions on how the music may be used. For example, FairPlay allows unlimited CD burns of single tracks but doesn't allow songs bought through iTMS to be played on other devices or to be traded on file-swapping networks. While anyone can use AAC -- it's an open standard, after all, and widely available for licensing -- FairPlay puts a barrier between Apple and the rest of the online music community because iTMS downloads can play only on iPods.
Business Week Online: Digital Music: Apple Shouldn't Sing Solo