I think it might be the audience. We are on a tech-focused website, with a vested interest in the Bay Area since that is where ycombinator is located, as well a

I think it might be the audience. We are on a tech-focused website, with a vested interest in the Bay Area since that is where ycombinator is located, as well as a good chunk of their user base. If you used sf on a Sci-Fi dominated forum it'd probably be read as 'sci-fi' the majority of the time.