I'm an app developer and 90% of the apps I've developed have been on contract and 100% of those have all been free. The strategy is either to have them support and extend an existing brand or experience with something mobile specific or to be ad supported. None of them have ever had a purchase price because, for a non-game (and even for a lot of games) that's the surest way to have no one download your app.
But, because I'm a developer, and know intimately what software costs, I've personally purchased around $300 worth of premium apps. I do this because they do specific things I need (like work as a micro-IDE, Git client, SSH client) and those markets are already tiny and I want to do what I can to ensure the developer is motivated to keep supporting them. But, even if there were a lot more people like me out there, it's tough to imagine an indie developer adding every feature every user could want unless they were in the top 5 selling apps of their category or it was a real labor of love.
What's surprising, in terms of feature parity is how big companies like MS or Adobe seem to care so little about it since they are on the subscription model and their goal is to be the go to for their categories on whatever platform.
Why doesn't Word or Excel, say, have more export options? These aren't dumb companies, so I imagine some of it has to do with use metrics. But then, is that a chicken-egg thing? People don't do it because they can't do it? Or can people not do it because the companies haven't seen interest in being able to do it? I don't know the answer, obviously, but I'd pay real money to see the MS Word or Excel use metrics, especially every time people bring up that they think the iPad isn't a "real computer" because they can't run the 15 year old spreadsheet they built with 100 VB scripts and 15 levels of auto format. Given that MS was a launch partner for the 1st Gen iPad Pro, I have to figure they know something about how their software is being used that has stopped them from prioritizing that kind of thing. But I don't know.