That's likely very true. I think most (if not all) women have learned that identifying yourself as a woman on the internet inevitably leads to responses like, "OMGRUHOT?!?!?!" So I don't blame them. I don't think that would be very likely here, though.
As for the topic, I think most people are simply going with the trends rather than being sexist. The fact is that most home brewers are men, and a lot of women don't like a wide range of beers. Those things aren't true for every woman, but are true when you take the entire population.
So you can't blame someone if they think your husband is the brewer or if they think you want a fruity beer. Or if you are out buying yarn and someone thinks it is for your wife, even. Presumptuous? Yes. Sexist? I don't think so. It's just as presumptuous to say that people are assuming women aren't brewers because they think women can't brew.
In my opinion, though, I don't think many home brewers would say a woman can't brew as well as a man. That would be sexist. And we all seem smarter than that.
And, as an FYI, the owner of my LHBS is a woman. I would like to see this hobby become more diverse, though. Being a computer programmer and a home brewer, I see enough men.
