I met a 50ish solo programmer a few months ago. His application handles an issue for a specific subset of nonprofit org (I'm probably not giving away too much if I say, churches). The app is not web enabled, it's not social, it doesn't run on ios android or mac. From our conversation I inferred he spends hardly any time on marketing it because he doesn't need more users. Yet he makes a comfortable living solely from the licenses, doesn't touch the app for weeks at a time, and adds new features on his own schedule.