Aside from the non-heterosexual market being large, there are two other factors:
1) JDate allegedly has nots of non-Jewish people on the site who are looking to date Jews. I mean, it makes sense -- it's a great place to find them :) Maybe there are non-geeks who are looking to date geeks.
2) My definition of nerd/geek goes beyond programming. A professional (in law or medicine or engineering) is probably way more interesting than a .NET corporate programmer. I could see "career/lifestyle tags" working for this.
Arguably it wouldn't even need to be limited to geeky activities, but general interest interests as well. Maybe someone really likes backpackers, or people who have completed Bioshock Infinite, or corporate M&A lawyers, or people from Surrey. Having verified tags for those things would make searches more interesting.
