I've previously purchased several apps (Pixelmator, Rivet, a few others I can't think of now) that are now available in the Mac App Store. Given that apps in the store are not allowed to use their own updating frameworks (like Sparkle), how will I get updates to them in the future? Can I somehow tell Apple that I already own those apps and get updates through the store? Or will the individual developers have to work something out on their own?
From Daring Fireball:
As reported in the Daring Fireball link: it doesn't work for some apps like Panic's Transmit, Unison or Coda. The licensing schemes used when you buy via the App Store versus directly from the developer are different and won't allow for it.
But this article from Cult of Mac has the author successfully updating a previously installed version of TextWrangler to the latest version via the App Store.
I disagree with the Cult of Mac articles conclusion, that "if you see something in the store that’s already on your hard disk, you shouldn’t have any problems installing a newer version from there" -- as Panic has directly contradicted that conclusion and they build and sell through the App Store so, pretty authoritative there.
I did talk to the developer of my favourite Twitter app, Kiwi, and he said he wasn't sure if the App Store could be used to update copies of Kiwi bought before the App Store came in to existence.
So welcome to the Land of Confusion.