I’m not sure I agree 30% is reasonable. Take the example of book publishing someone mentioned earlier, someone has to proof read, edit, lay out, print and ship physical books. What does Apple actually contribute in the App store? It’s essentially hosting a very small file for download and processing card payments. Is that really worth half as much as a developer coming up with an idea, writing code, testing etc? It’s been shown time and again that the only “checks” that are effective in the app store are censorship and enforcement of anticompetitive rules, so I don’t buy the security argument. People only need that hosting because Apple prevent downloads from developers directly, also anticompetitive.
I’d say 5% would be more appropriate, and I’m being generous.