That said, the lack of a paid upgrade option in the App Store is a significant negative. To pretend that a one-time purchase for $5 should guarantee you a lifetime of upgrades is both shortsighted and abusive to developers.
Buying Office 2015 only gets you that version.
If you want Office 2017, it's not an 'update' per se unless they generously offer it to you, but rather an entirely new piece of software.
I've seen it upfront two times in the playstore, where apps I liked released a new version. I was eager to buy the new version but the new/updated reviews for the old ones were ruthless. One app had to give the new version for free. The other had to promise to keep updating the old version too. The first team just gave up on both apps. The second team (one developer actually) continued but slowly toned down his efforts, going into essentially maintenance mode.
As I user I've had the opposite problem: developers who radically change an app that was perfect. I have no way to revert to the older version I preferred. If the developer had created a new app, I could have stayed on the old one. It's unfortunate most other users want unlimited updates. Paid upgrades and version selection remains an unsolved problem.
The lack of an ability to trial iOS software with no financial risk means that the risk of purchasing crappy software is priced in to the amount people are willing to pay. Think of it as a weird sort of reverse insurance. Every iOS software developer is "paying" (via lower prices) customers for insurance against crappy software and, unfortunately, there is a lot of crappy software, so the premiums are sky-high.
Apps that can show me a video or even a pictures/animations of the application in action I would also be likely to pay for. More often than not, though, I get treated to a powerpoint presentation or a short 3 sentence brief about what the app does that barely describes anything. And I also have no idea about the app’s stability or the likelihood of continued support. So how am I supposed to just trust that I’m getting $30 worth when I buy your software?