Given the relative gender disparity in the technology field, it's easy to make the assumption that any given developer is a man – we all do it sometimes! It's useful to have that pointed out when we're wrong, so that we can be reminded that we sometimes make incorrect assumptions, and eventually it hopefully won't happen as much.
None of the comments along those lines have been needlessly faux-offended, or attacking anyone – just pointing out a mistake that it would be good to rectify. It's really not harming anyone :)
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.
It's not nice to assume "he" to always be the default - that is what was being corrected. One did not have to know that "she" was correct, but it was easy to find out that "he" was probably wrong. Let's keep discussion on topic, rather than venturing into talking about what you're "allowed" to do.
Getting the obvious gender right is a matter of courtesy.
The internet is replete with opportunities for getting triggered and starting flamewars. For HN not to sink into a deeper circle of hell, we all need to resist these temptations. So could you and everyone else please not take HN threads on generic, divisive tangents in the future?
It does get extremely boring to read on every article written by or about a woman someone correcting every comment that uses "he" as a generic antecedent, but in the future I will just ignore it instead of inciting a potential flamewar.