OP: I think you're right. I don't think it's deliberate, but particularly with those examples you mentioned there is a definite bias. Perhaps some of it could be explained by laziness - having to write, code and voice-act things for both male and female characters does increase workload, at a time when publishers are pressuring developers to pop out games faster and cheaper.
There is something to be said, also, for the objectification argument. I've heard it described as "Male characters are designed to appeal to men as someone they'd want to be. Female characters are designed to appeal to men as someone they'd want to sleep with."
I don't think it's necessarily harmful to make female characters attractive, even specifically sexual; what I do think becomes harmful is when there's such a broad gap between the portrayals of male and female characters. (Prime example: the idiotic cleavage window on the average suit of female armour in games. And movies. And on TV. And in comics.)
Actually, you know what? Stick a bit of code in there. Have two versions of each set of armour, and two character models for each character. Let the player select their sex and orientation along a five-point scale - all straight, mostly straight, either way, mostly gay, all gay - and simply interpolate the outfits and character models so the characters they're attracted to are physically attractive while the others are plainer. That way the "romance options" are attractive - objectified, if you like - regardless of sex, while the others aren't.
I am joking, of course, but at least part of me thinks that it could work... ;-)