Wil Shipley wrote an article on why developers like him need paid upgrades on the Mac App Store (and also on the App Store for iOs).
What we would like to do charge $20 for version “2” customers upgrade to “Delicious Library ∞,” but still charge $40 for new customers.
Now it’s not possible to do that on the App Store, but you can do that by yourself, selling the app from your own website, but doing so you’ll lose all the advantages o being on the App Store, especially those regarding the updates and visibility.
It’s weird that Apple has still to figure out a way to let it work, I’d suggest allowing discounted price for the ones who have bought the previous version 1.
So, for instance, as a developer I could say to the Mac App Store, “When someone buys ‘Delicious Library ∞’ who have bought ‘Delicious Library 2,’ it should cost them $15. Leave our version ‘2’ page up but don’t allow any new sales of it, and mark it as obsolete.” (In this way existing version “2” customers can still be updated (for free) with bug fixes even if they don’t upgrade to “∞.”)
You should read the full post if you have the time.
Which now is not possible because Apple doesn’t share with the developer any data about users, so they can’t know if you have really bought that app in any way ↩