As mentioned itunes have done this very well with music, movies and apps. Because Apple gets most of the revenue from the physical devices, they are able to let the price of using Itunes be relatively low.

This in turn makes it easier for content providers to create a balanced mix of free and paid. Which in my view is the key to succeeding in the digital economy.

If Amazon and Sony are able to emulate this possibility, they will be blown out of the water once apple hits the book/newspaper market.