No, this is not a male-only website. In fact, most of the other staff I know are actually female. Brony is just a unisex term, since the word "Pegasister" had a very short-lived life - everyone knew the word "Brony" more, so females just conformed to using such a word. This is the case with approximately 95% of brony websites, as the most commonly searched term for the My Little Pony fandom's name is "Brony".
In short, Brony is the more popular word that everyone searches. Because of such, nobody uses Pegasister anymore.