Like the credit card processing, the hardware manufacturing facilities in China, the software libraries, the industrial designers...
Apple has made it absurdly convenient to consume rich content. They have built fucking science fiction. 30% to get delivered to someone anywhere, any time is a bargain. You're paying to be part of the gut wrenchingly difficult channel Apple has created from scratch, which no one else had the foresight to predict or the balls to put money behind.
Apple bet the damn farm on this crazy iDevice shit and they get to charge whatever they like for it now that it works. Anyone who doesn't like it can go build their own fully integrated platform.