That's why I qualified it with "native" - the US has by far the most English-as-a-first-language people. In my head everyone speaks like an Anglo guy from Idaho, and since HN is text-only, metaphorically speaking the lights are out, so I'm left without a clue where other people are sitting or where they are from.

In other words, if you found yourself in a dark room with a thousand English speakers who all sounded like Jesse Pinkman, what country would you assume you were in?

I would agree with that, at least for this site. I wouldn't be surprised if the ratio was 1 to 10, since tech skews it significantly. For example, I work in tech in the US, and the only American I've spoken to today was my summer intern, and - oh hold up, I just typed that and realized she's from Canada. OK, I've been in work meetings all day and I have not spoken to a "US American" during that time. I suspect that other sites, particularly some subreddits, are mostly American, though.