For example, if Apple put out a sexist ad, you can bet people would talk about sexism in BOTH the tech industry and in the ad industry.
"Tech" is considered by the mainstream to be full of socially maladjusted overgrown boys who spend far too long in their mother's basement. They are cold and unemotional and they took engineering classes in college; perhaps one is the cause of the other. Sexism in programming teams made up primarily of this stereotype is a common topic here, and it is almost universally agreed that it is a major problem.
So I guess it annoys me when a bunch of marketing people use sex in their advertising, as they do in every other industry imaginable, and we use it as an opportunity to flog tech some more. Where the exact people who made this decision selling umbrellas instead of hard-drives, would this be on HN? I don't think so.
1) The ratio of males to females is worse. Women feel more like outsiders in tech than in other industries. Things like booth babes make us feel like outsiders because they are a ploy to attract MEN to the booth, as if there is no reason to attract women to the booth. Secondly, as a female at a conference, people assume I'm not the technical expert. They ask me if I'm in marketing. I see them directing technical questions to the males. It is really annoying to be judged based on your looks and gender, but I don't blame them, because chances are they are right due to the scarcity of female technologists. Booth babes reinforce the stereotype that women at the conference are there because they look nice and are friendly. That makes the problem even worse. Objectification in general reinforces the idea that a big part of women's role in society is to look good.
2) Tech is an area where people STILL question if women are really as capable as men. That makes women in tech more sensitive to gender bias.
In other words, it just stings more to see this coming from a tech company.