I am not sure if you have ever been on the other side of this, but having people constantly assume you are a man because you know how to program and you're on the internet gets very old, very quickly. You can either accept being constantly referred to as a guy, which becomes flat-out alienating, or you can speak up for yourself, in which case you get responses like the one you just wrote.

I get that the gender of the author doesn't matter to you, and it may not even matter to the author of the article, but it does matter to a lot of people. No one is suggesting mistakes are a grave sin—even if her blog does say "Julia Evans" in giant letters right at the top. If someone makes one though, the correct response to people pointing it out is to accept the correction and keep it in mind for next time, not to accuse them of spam.