That would leave app makers susceptible to a major player with large amounts of capital that can sell at a loss until all other players are driven from the mark

That would leave app makers susceptible to a major player with large amounts of capital that can sell at a loss until all other players are driven from the market and then raise its prices once it has gained pricing power. Book publishers appear to have wizened to Amazon's game here and have refused to allow Amazon to use discounts to drive other sellers out of business. Many publishers have moved to an agency model where Amazon takes 30% and the publishers set the retail price of the books.