Apple’s use of aac afforded Apple the ability to create a proprietary hardware delivery system. This offered advantages to Apple, which could avoid interoperability, and advantages to its DRM-oriented licensors. As time goes on, Apple’s market dominance reduces the need for DRM, and will soon reduce the need for aac.
The day will come when people stop rewarding this kind of behavior. But this day has not yet arrived. I run into people who don’t see why the acc/iPod has been so counter-productive, with the counter-argument they raise being the mp3 compatibility of the player. But aac and its use to perpetuate iPod’s dominance has been a truly unfortunate use of “hardware DRM”, motivated by
profit at the expense of the consumer.