An annualized revenue of $110k for a $5 app that does nothing but let you draw black rectangles (or blurs, or pixelate) parts of an image? That sounds remarkably good to me...
Even with sales falling off, it sounds like he did pretty well for an afternoon's work.
I'd say you're missing the point. The point isn't about this poor developer and how hard he's having it; the point is how barren and forgotten the Mac AppStore is.
It doesn't have most of the key Apps most Mac users use every day - things like Skype, Office, etc. Some of the Apps which I used to own via the MAS have actually migrated away from it because of sandboxing restrictions which even close work with Apple couldn't solve (e.g. Coda).
I use Sublime Text quite a lot. If it was on the MAS, I would pay for it and the developer would earn a living from his hard work. As it is, it's too awkward for me to donate and I'm more comfortable being a customer than a donor. That developer hasn't seen any money from me, which is a shame because I pay for plenty of Apps which I value much less.
I don't know why he hasn't uploaded it, why Microsoft hasn't uploaded Skype, etc, but that's a big reason why the AppStore is so barren: it's irrelevant. New users shouldn't go to the MAS and expect to find the Apps to get them started.
It's a forgotten wasteland. It's missing many of the features from the other iTunes stores: you can't even gift Apps, for example. I tried to gift a copy of The Sims to my sister and there's just no way.
Yeah, the Mac AppStore is a barren place where nobody finds what they want and utility Apps like this one can enter the top charts. It's Apple's fault - they haven't kept the store up-to-date, and they haven't done enough to ensure that new users can quickly get themselves setup with the most commonly used Mac applications straight from one place.