In explanation, you join the iTunes affiliate program, which gives you a 7% cut on sales in the app store. I really don't understand why this isn't more widely known.
It's like shooting off my nose to spite my face, I guess, given the growth of the mobile market, but I truly hate the shape of our industry these days, when it comes to how indie developers are able to connect to their users...yes, it's better than it's ever been, but not because of Apple. It's better because of the open web, and Apple and Google are using their near-monopoly powers to impose the old gatekeeper model long past when it should be relevant.
Even if I add advertising costs (because some people allege the app stores provide a customer base), it's still less than 20%. But, I could distribute dozens of times the amount of software I'm selling with the same hardware and colo (if the market wanted to buy dozens of times the amount of our software currently sold).
So, it's true that there are costs no matter how you sell your software to customers. And, I might be willing to pay more for things that would make my customers lives easier. But, 30% is...it's just outrageous, to me. Apple and Google are among the richest companies in the world. Their margins on running these stores is obscene.