The interesting thing is, Apple originally intended that this should be the goto way to get user generated applications on the iPhone.

But then, the jailbreak scene came up and somehow Apple changed their stance by creating the app store and thus the possibility to control what kind of native applications will run on the devices.

Of course this way has the advantage of not needing a paid developer account or need to have the app approved by Apple but then again, such a webapp is harder to monetize if that's what you are after than to simply write a native app and sell it in the app store.