> Or a free app that is just done as a thank you to the community that has supported them over the years? What would be wrong with this?

That would be a very expensive thank you for a tiny business! Given Panic's level of polish and concomitant development timelines, I expect this app took several months of a designer's time and at least six months of an engineer's time—probably more like nine. Then QA, support, etc. I'd guess we're looking at a >$150k price tag here, plus ongoing maintenance.

As to paying for itself via bringing new users into their customer base: given the average sale price of their desktop software, this iOS app would have to generate several thousand net-new sales. That doesn't seem wildly outlandish to me, but I'd guess one order of magnitude fewer is more likely.