I'm surprised they consider OS X to be a good platform from a business model perspective. How can you build a sustainable software business without paid feature upgrades? The first review of Sketch 3 on the store is an underserved one star complaining about the way they've handled the transition to Sketch 3.
The app store model works fine for throwaway impulse purchases but that seems like that's about it. Per-unit prices seem to be racing to the bottom the same way they did in the iOS app store too.
You release a new version as a new app and your users buy it again, if they want to. It does away with 'upgrade pricing', but the idea is you just reduce the base price of the app to compensate so there's a slightly lower price for new purchasers, but a slightly higher price for upgrades. It's a different simpler pricing model, but not an inherently un-viable one.
This is nice enough in theory but in practice it doesn't seem to work out so well. Just look at the ridiculous backlash the developers of Clear suffered when they had the temerity to charge $2 for a major update.
You're also penalized in search results and app rankings if you have several distinct apps scattered through the store instead of one app with a long history of reviews and updates.
Given the thousands of products in the App Store that do quite well (and given that Sketch 3 was the highest grossing app in the App Store yesterday) I think your examples are anecdotal at best.
The app store model works fine for throwaway impulse purchases but that seems like that's about it. Per-unit prices seem to be racing to the bottom the same way they did in the iOS app store too.