One worry is since iOS is so dependent/tied to the app store for updates or reinstalls, if the developer pulls the app from the store, you can never redownload

One worry is since iOS is so dependent/tied to the app store for updates or reinstalls, if the developer pulls the app from the store, you can never redownload it, and you are then stuck trying to maintain a copy that you backed up and hoping you don't lose the file. And if you don't plug in to a PC you wont be able to reinstall the app. This happened to me with smule and "Magic Fiddle".