> 1. Developers can't offer free trials, so I have no way to test out an app and see if it's worth $$$$$.
Yes they can. Via in app purchases, they can offer a reduced set of features for free, and the full set for money. As an example, I have Working Copy (free) but have (twice now) done the in app purchase to unlock "pro" features because I've found enough utility in the software. It will work without the purchase, though, and is perfectly fine (no one, in person, that I've recommended it to has ever paid for it, but still use it).
> 2. Developers can't offer upgrade pricing, so I may have to pay the full entry price again in a couple of years, particularly because...
At least some have worked this out. Buying OmniFocus 3 (?) with OmniFocus 2 (?) still installed on your device got you a discounted price. I'm pretty sure that Scrivener did the same, but don't quote me on that. I purchased it a long time ago.
> 3. Apple's yearly OS updates break or create bugs in existing apps all the time, which means no amount of up-front developer testing can ensure a truly stable or long-lasting end product. These iOS updates are required to continue receiving security patches, and if I upgrade and discover a critical app broke, downgrading is impossible in almost all cases.
That I can't disagree with.