My bad, I had assumed AAC was the DRM technology for iTunes. I can't find the name of the DRM technology - nonetheless, iTunes files are rights managed.
Case in point: Only iTunes and iPods will play files purchased from iTunes. Media Player, Winamp and every other mp3 player on the market will not play the files downloaded from iTunes. Having to burn an iTunes song to a CD, rip the CD and then encode it to mp3 so that you can play it on an mp3 pda/cellphone, Dell Jukebox or on a buddy's computer gets to be a pain.
Napster has similar DRM but many more devices can play DRM 10 files. With iTunes, only Apple products will ever be able to play iTunes files.
An interesting note:
In the last couple of weeks holes have surfaces allowing Napster and iTunes users to bypass DRM. Both Napster and iTunes closed the holes in a matter of days.