It's bad for consumers to the extent that iOS and Android phones aren't interchangeable, and that's a very large extent.
> what do you think is a reasonable fee for Apple to charge?
That's an interesting situation, because if the game was free Apple would charge nothing. And the more they bang on the drum about consumer safety, the more I want them to charge a fee appropriate for payment processing.
If I was just arbitrarily setting the fees, I might go with something like 25% of the first 20 dollars per app per user, and then 5% afterwards.