Whether it's gender, rudeness, or something else entirely, I gotta admit, it bugs me when guys hold the door for me too, IF it's a situation where they wouldn't hold the door for another guy. And I almost NEVER have had a woman hold the door for me in those situations (maybe it's just the culture around here, idk). Plus, in the elevators at work, the guys let the girls out first even if they have to step outta their way to do it. I have not seen them do that for other guys. The days that they don't look at me and wait for me to get off first (or say "go ahead" with a courteous smile) are the days I feel like I'm passing alright.
And I hold doors open for everyone regardless of gender in SOME situations, but you gotta admit people, there are some situations where holding the door for the next person is just courteous, and some situations where you're going out of your way to let all the ladies go first or whatnot. That's where the difference lies in my opinion. If you're holding the door just that little bit more as you go through it, that's courtesy and applicable no matter the gender. If you're holding the door open and stepping out of the way while the other person goes first, in my opinion, that's a different level of courtesy reserved for men being gentlemanly towards women.
For instance, when I drive a friend somewhere, if it's a gal, I'll go to her door, unlock it and hold it open, then go get in my side. If it's a guy friend I wouldn't dream of doing that. I just unlock the car from my side and they open their door and get in at the same time I do. Call me sexist if you wish, but the women I've done that for all appreciate the "courtesy" of it, and I can guarantee you the men I hang with would think it was messed up if I did that for them. Just how my friends are? Maybe, but I think it's more along the lines of "some courtesies are for everyone, some are just for women"...
And... commence veggie-flinging.