Apple spent millions of dollars promoting the concept that iPhone/iPad apps should not necessarily be free. How many times did you see a print ad where they showed a bunch of cool apps AND their prices? This 30% fee is simply a return on that investment. Paid apps don't sell on other platforms (e.g. Android) because these platforms never marketed this idea to consumers. 70% of something is better than 100% of nothing. It's the same story with iTunes -- Apple is the only company that convinced consumers to pay for music, and they charge exorbitant fees to the record labels.