Separate to my other comment, I should acknowledge that this seems overwhelmingly true. Dwarf Fortress is famous, but I've learned recently that there are also thriving communities for Cataclysm DDA, Dominions, Aurora, every imaginable Nethack derivative, and half a dozen other equally-opaque games.

As long as the genre or mechanics are new, there seems to be a (limited, but) perpetual apatite for ludicrously deep games with minimal player handholding.