Presuming a poster is male when no gender is given is statistical discrimination (not a bias).
Most Less Wrong users are male.
X is a Less Wrong user.
Probably, X is male.
What, if anything, is biased about this pattern of reasoning?
Correct, that is another instance of the same reasoning pattern with high inductive probability. I see no evidence of cognitive bias in either case.
Recently, I have noticed a cultural bias for the United States running through LW threads. It is perhaps to be expected of an English-language website, but for one that is about, among other things, overcoming bias, it is important to recognize one's own.
Aspects of the bias I have observed include:
I'm not the first to raise such concerns, either.
By comparison, e.g. the English Wikipedia strikes me as an example of an international English-language project that's relatively successful at recognizing and fighting systemic bias, and a whole set of template messages to mark articles with identified problems.
To quote Wikipedia itself:
The reason I haven't mentioned other obvious biases, such as gender, age, education, or First World biases, is because those (in my experience) tend to be more subtle here on LW and because I'm myself subject to some of them. However, I might cook something up on them later.