Gamasutra has a lengthy (10 page) but interesting interview up with Tarn Adams, the programmer behind Dwarf Fortress. The interview touches on a lot of issues: the history of Dwarf Fortress and how it came to be, game mechanics, the follow that's sprung up in the game's wake ...
What's left to answer is why'd we be so into doing a fantasy game. That's probably the same as everybody else: Tolkien, D&D, myths, and of course, the movie Beastmaster. (We like the part where the evil priest is like, "You'll be sacrificed to 'The God of AAaa,'" like they didn't even bother thinking of a name, just powering through on the power of their badarsedness.) But there were all kinds of things like that. In the movies, books, the arcade, PC, consoles, we were surrounded by that sort of thing.
It's an interesting, if lengthy, interview and worth a read through. The community that's sprung up around the game is almost as interesting as the game itself, especially the bits and pieces that have become popular outside the Dwarf Fortress community.
The Making Of Dwarf Fortress [Gamasutra]