These crazy outdated licenses that let you print as many magazines or books you want forever, for a one-time price. But if your hobby is making apps, then suddenly the same font will cost you 50 times more - for a single year.
I guess these font sellers imagine there’s still some app boom - a Klondike rush with developers bathing in dollars. Maybe if their licenses were more realistic, piracy would be less of a problem.
I'd argue that complaining about font prices is less like a Hermes bag, and more like complaining about high-end ingredients when a supermarket has cheap stuff. Yes, you can get away with cheaper materials when cooking, but the final product will deeply suffer.
If you can't afford the license for the font, your app is small-time enough that you can make do with one of the many, many high-quality fonts that are available for free, there's no need to pirate it. If your app is big enough that the difference matters, then you can likely afford the sticker price.
All I have done is defend the importance of typography, and never mentioned piracy or stealing.
You won't notice many small differences between certain fonts. But that doesn't mean they're unnecessary. As you said, they make a difference when taken together. For screens, there are a number of adjustments and techniques that improve screen readability. Hinting, separate designs, contrast for low dpi and subpixel rendering compatibility, for example. At least some of the optimizations don't work out of the box, but have to be adjusted by designers. That's why it can happen that a font you bought for print media now requires an extra license for websites and apps.
There are plenty of wonderfully readable fonts for the web and apps that are free and sufficient for most projects. If you want something special, I don't think it's wrong to pay for it. Personally, I would prefer more reasonable prices, though.
But the differences on the lowercase "t" and "s", uppercase "g", the number 3, and both upper an lowercase "c", are obvious. Helvetica is much more refined.
There are good reasons why well designed typography is expensive. A lot of thought and effort went into designing every line and curve. Even if most people can't consciously appreciate these details, they experience it subconsciously by how the design makes them feel. This is why brand designers are well paid. Anyone can design a logo, but to make a design that transmits a specific feeling, that requires a lot of skill. And typography is a core component of this.