From what I understand the iOS App Store doesn't support that model. I've heard complaints from developers who have used that model with success on the Mac, and are frustrated that they can't do so on iOS.
There are apps using this though. Two that ring a bell for me are Agenda and Hook though only the first one has an iOS app that also utilizes this model.
I assume they give each feature a date of availability and compare to the last purchase made via the App Store receipts and make features available or unavailable based on that intersection.
Edit: Edited for URLs, I wish this stupid site would support at least basic markdown... So mind-blowing it doesn't.
It doesn't explicitly support but today people work around it with one-time in-app purchases for all the functionality. Two apps I can think of doing this are Halide and Darkroom.
But yes, you can't just pay $X upfront in the App Store directly. The app makes you this offer, not the store. I agree it's not ideal.
I assume they give each feature a date of availability and compare to the last purchase made via the App Store receipts and make features available or unavailable based on that intersection.
Edit: Edited for URLs, I wish this stupid site would support at least basic markdown... So mind-blowing it doesn't.