You may be pointing out a problem with English. "Programmers" could simply mean more than one programmer, but there's an implication that all programmers have those problems or perhaps that the problems are pervasive.

I get the impression that these are mistakes that someone has seen (or made) at least once. Some of them may mostly be made by programmers who are beginners.

I agree that it would be nice to get percentages, even if there are large error bars. I think the main point of these lists is to warn programmers that they may need much more specific knowledge than they think they need. For what it's worth, the commenters on those lists are programmers, and I'm not seeing comments which say "That never happens!".