This MacWorld article is an excellent corrective.
Macworld: Editors' Notes: As the tech world spins...
... AAC (a.k.a., Advanced Audio Coding, MPEG-2 Part 7, or MPEG-4 Part 3) is an industry-standard audio compression/encoding technology developed in cooperation by AT&T, Dolby, Fraunhofer, Nokia, and Sony. Notice who isn’t in that list: Apple. Also notice who is in that list: Sony.
... Sony has actually supported AAC for some time. Sony Ericsson mobile phones have supported AAC playback for at least a year or two, and Sony’s PlayStation Portable has supported AAC since a software update in July 2005.
... iTunes Music Store tracks aren’t standard AAC files; they include Apple’s FairPlay DRM technology to restrict playback to iPods and a limited number of computers running iTunes, and Apple hasn’t licensed FairPlay...