It's encouraging to hear this can work. Of course that guy was extremely fortunate to be making something everyone was interested in, so it's still a risk (but then again: what isn't?).
There was no fortune to it, it was years of OSS work on lots of Ruby projects followed by a realization that existing solutions were terrible and I had the knowledge to make something better. Nothing like years of experience to put you in the right place at the right time.
You say fortunate, I say foresighted. In any event. I imagine that he started building it to meet his own needs and the growth of revenue now is a happy side-effect.
It's probably always a bit of both, but I'd say that level of success doesn't come without the necessary context (several things have to conspire for it to happen). Anyway, it's an inspiring story!