The only place that AMZN has high margin is cloud computing, but the competition is coming now. More players are getting into the space. Companies like Oracle, IBM and Microsoft can leverage their Apps that sold to the customers.
Retail business is low margin, digital products are low margin too and a lot of competition. The business model of selling Kindle Fire at the cost and making money from selling contents will not work. It's just wishful dream because people buy Kindle Fire from Amazon are price sensitive, mostly have no loyalty to any stores(only have loyalty to the price).
Amazon keep selling its growth story now. Its valuation based on its growth, but only from revenue aspect, not from profit aspect because most of its business are low margin.