I guess it really does come down to, to each his own. I wouldn't expect anyone other than my sub to call me sir. Basically, I see it as a sign of submission and if someone isn't submitting to me I don't see the need for her to call me sir, even if she is a sub in general. But everyone has different tastes. I do agree though that using sir as a default term of address is overdone. I'm glad that doesn't seem to be done here.