In addition to Google's own app marketplace, Amazon, Horizon and Vodafone have all announced that they are creating their own app stores for Android. So there will be at least four app stores on Android, which customers must search among to find the app they want and developers will need to work with to distribute their apps and get paid. This is going to be a mess for both users and developers. Contrast this with Apple's integrated App Store, which offers users the easiest-to-use largest app store in the world, preloaded on every iPhone.
Not to argue with The Steve or anything, but if a single app store, controlled by a single corporate entity, is better than many, then I guess we also need only one web site, and only one newspaper, and only one political party. Apple's classical "1984" commercial is getting more and more ironic.