When the App Store was launched, Steve Jobs said they plan to run it at break-even, no profit, and for quite a few years that was exactly what they did. Now they are profiting from the App Store and clearly could continue to run it as they do on a lower percentage, but I don't think 10% is that number. If they could run it on 10%, they wouldn't have operated it without profit for the first quite-a-few years at 30%!