Just like everything else, AudioUnits is a way for Apple to make more money and make life harder on anyone who's not 1000% brand loyal.
As far as I'm concerned, with their latest rash of acquisitions and the recent decisions they've made on software/OS pricing, services, and supprot for standards, Apple is the new Microsoft.
You heard it here first, and I can absolutely guarantee that many more Mac users like myself will say it more and more often as time goes on.