Jeff Scott:

The lack of an ability to download previously paid for digital goods, in the case an app, is the real problem. In the world of digital distribution, one where we are moving to a cloud-based backend and a Post-PC world, the apps and other digital media you buy in the App Store, you expect to be available forever. But the sad truth is, they are not available if the developer chooses to pull them. There are hundreds of thousands, perhaps even millions of Tetris for iPad users that will find that out next time they upgrade devices and try to download the app.