I'd like to think this is on par with the "no children" idea. While lots of us would love to have children in the game for realism's sake, it won't be right because of the potential to abuse them, or they'll just be tacked onto the game and break immersion because of how little they'll add to game play.
You know, I don't want to play a game and be abused because of my gender - to be cat-called, constantly hit on or to be told "You're a woman. What the hell are you doing fighting things?!". That's the kind of behaviour you'd want to be implemented because of gender differences. As mentioned before, it will get old fairly fast and be offensive. If this were a true medieval setting, women would not be a playable character - we would not be able to go out, fight things and conduct Thaumaturgy without the world wanting to hunt us down.
I can't comment about Mass Effect, because I've never played it... but I just think that they shouldn't change anything to affect one gender more negatively than the other. If they can think of something that'll be more "Oh, that's interesting" and dependant on, let's say, biology than tradition, rather than complying to stereotypical gender roles, I'd be more willing to support that. Traditional sexism is something we're trying to get rid of in the modern world - it isn't something we want to continue to endorse in the form of entertainment by trying to make it an accurate historical representation.
EDIT: Sorry, I was typing this before Tony posted his comment directly before mine. This post is referring to a general attitude of sexism in the universe, which is what people seemed to be exploring.