I've read articles saying that Amazon's App store does this. i.e. if they see you selling your app cheaper for iOS, they can go pricematch it. Or, if you give it away for free, Amazon can do the same thing an pay you nothing (since a percentage of zero is zero). AFAIK, Apple won't do the same thing, they'll just reject your app if it uses the wrong APIs or competes with a market they want to own in the near-term.