Charging up to 30% just for putting something in an App Store is inexcusable rent-seeking behavior. Apple are a bunch of money grubbers with a captive audience.
Yes and Target charging the same for the products they sell should be criminal as well. We deserve everything for free! Certainly apple makes money, and their margins are well off, however they do a lot for those apps. They are scrutinized by teams of folks keeping us safe. They host, and dispense terabytes of data each hour for downloads to peoples phone. They host the website and update the contents to ensure it is safe. They assist in troubleshooting app issues between the OS and the developer to aid in updates. I'm not sure 30% is a fair value considering a $10 app and a $100 app would incur similar costs yet one would pay more. All things included they deserve some kind of compensation for hosting the store, app reviews, bug detections, and the digital hosting assets.