Fixing the paid app update problem
One of the major criticisms of the iOS app store from developers is how to deal with paid app upgrades. If someone makes an app, they get paid that one time. However, if they spend another year making great additions to that app, it is given free to people who have bought the app, despite new features added.
This runs counter to most software development revenue schemes. Where, you buy the newest version of Photoshop (or at least you did until the recent switch to subscription software!) each time a version comes out. This is not possible on the iOS app store, at least not easily.
A developer could put out say App 12, then App '13. But they are left with the dilemma of whether to remove 12 from the App Store. You don't want people accidentally installing an old version. Further you cannot add upgrade paths for cheaper upgrades to users who owned your older version. They simply have to pay full price for the new app just like any other user, which seems a bit unfair.
The arguments are laid out well in this blog post: http://blog.wilshipley.com/2012/03/mac-app-store-needs-paid-upgrades.html
However. I noticed something in iTunes yesterday. Note the emphasis on "free" in the app update screen. I'm putting forward the theory that this emphasis isn't accidental. While, it is true, it could be just a reassurance to casual novice users that they aren't being charged anything. I think instead, it is going to be a clear differentiator when they announce and add "paid upgrades" to the iOS app store.
I think developers will soon be able to fork their apps, so that they can add a "paid upgrade" to go from 12 to 13 for a reduced price, while still being able to offer the app at version 13 for the full price. This would allow them to simply replace the 12 version, instead of keeping it in the store as some confusing legacy app.