Nobody argues that this is not scientific research, but that doesn't mean it's not interesting or useful. It also violates some of your expectations: the majority is not in the US, India is underrepresented despite English being their second language. And if i might add, despite their national focus on entrepreneurship, the UK numbers are low.
It also violates some of your expectations: the majority is not in the US
My tentatively expressed expectation was written in my post (grandparent to this post) as "So it wouldn't be any surprise if a plurality of participants on Hacker News live in the United States, and a majority live in countries where English is a routine language learned in secondary education." The word "plurality" does not mean the same thing as the word "majority." So far the poll results (which, for reasons I mentioned in the grandparent post, should not be taken as the last word on this issue) show the sum of "United States - NYC and SF area" and "(Rest of the) United States" comfortably outscoring any single country mentioned in the poll, which fits the definition of "plurality" for these purposes. But, yes, we have no idea where most HN participants live, and we have no idea who comes forward to answer yet another HN poll as contrasted with HN participants who use their HN time to discuss more verifiable factual issues.
As I'm writing this the numbers are 2186 for the US vs 496 for the UK. The US population is almost five times the size of the UK, so the UK is actually overrepresented compared to the US.