It's the fundamental difference between functional illiteracy and "plain" illiteracy.
This difference shows up all the time when analyzing data because some jurisdiction will only report the illiteracy number while some other will include the functional illiteracy as well.
Proving someone "tried* is also [nearly] impossible here: just take standard test-taking strategies for standardized tests of reading comprehension, and apply them to this context (because that's all this is, but not even done by people whose entire job is to make "good" tests)
I rarely read the articles posted on HN. The discussion is frequently much more interesting and often more enlightening. I generally only read the article if the filter of other people's comments suggests that it would be worth my time.
I think I am probably not alone in this.
I have fantastic reading comprehension from a standardized test point of view - I was always able to finish the section well before the time limit. But I also knew I didn't have to actually follow the directions - I didn't need to read the passage, I needed to find the answers: a very different, and far simpler, task.
That's what this would become.