Since quite a few people missed it the first time around, and I don't feel like typing it all out again on my Droid....
Ok.... This is how it is in the Star Wars Universe.
Sir: A term of respect in the militaries of both Republic and Empire for a superior officer. It doesn't matter whether that superior officer is male or female. No distinctions are made.
Lord: Term of respect for a Sith of either gender. No distinctions are made. The only time a Sith is termed as "Lady" is if she's married to a Sith Lord. Lady Grathan, for example. She's married to Lord Grathan, so to distinguish her from her husband, she is referred to as Lady. If, however, she had chosen to keep her last name, then she too would be a Lord.
Master: Term if respect and rank within the Jedi Order for either gender. No distinctions are made. In the rare instance of a Jedi/Jedi marriage, and both are of Master rank, they are then referred to as "Master" followed by their First names. Or if the wife doesn't wish to take her husband's last name, they can both still be referred to by Master and their last names.
I can't quote sources here, since I merely observed the practices in the old comics, novels, movies, and ingame. Use deductive reasoning and yes, I actually applied common sense to Star Wars. I know, it's almost futile, but sometimes it DOES make sense.