On a related note, one of the technical details about the Mac App Store that I find interesting is the fact that once an application is downloaded to your machine, there's nothing Apple can do to revoke that copy. It sounds like steam manages the licenses of your games for you, whereas the Mac App Store bundles the receipt into each copy of the application that you download. Apple could in theory deny you access to future updates of an app, and you wouldn't be able to use that app bundle on a different machine, but they can't deny you access to an app once its been downloaded.