They get their 30% subscription fee. And they get to control the customer relationship. App publishers have a really shitty deal here.
Mobile computing would be so much better for competition if this had become a Microsoft / Google duopoly rather than have Steve Jobs with his perverse app store model. We'd have web downloadable apps and a better mobile web.
We now have a cartel for 50+% of American consumers. The cartel is so greedy that it's now placing ads to confuse and ensnare consumers even more.