Steve Jobs stated at D8 that the app store is a revolution. I thought he was overselling it, but app store is a revolution because people install apps without the fear of it screwing up their phone. It's rare I download an application to my pc and run it. For fear of crashing the computer, corrupting the computer, compromising personal information, pop ups, degraded performance, being in a botnet, viruses, etc. Those fears are mitigated in the apps store. Here are the reasons:
1 The app store is the first time a large, reputable company vouched for the integrity of hundreds of thousands of applications.
2 the lack of multi-tasking (and now true multi-tasking) ensures rogue apps don't waste your cpu cycles, and degrade performance.
3 the sandbox ensures apps can't affect the files in other applications. Users can't even mess up the files since there is no system file browser.
4 the uninstall process is handled by the operating system. you don't have to worry about the app not uninstalling properly.
5 the login/purchase process only involves entering a password. this reduces the overhead of entering all your payment information to buy an application.