Subjective quality of writing, and objective quality of communication, don't correlate all that well with reading level. Pretty much all the popular readability formulas use fairly simple functions of sentence length and percentage of hard words (i.e. not on a minimal vocabulary list), so prioritizing clarity and accessibility will tend to push readability scores down.
I just ran an arbitrary selection of articles from the New York Times and San Francisco Chronicle through a Dale-Chall readability metric here; the results varied between 9th grade and a college sophomore level, with a median of about 11th grade. The most recent chapter of Luminosity scores at 9th or 10th grade level, while the most recent chapter of MoR lies at 7th-8th.
There's been a recent heavily upvoted and profusely commented post about things people want to learn. It's close to having so many comments in a single day that it should probably have a part 2.
However, the subject seems to inspire thoughts about what *other* people ought to know, and while that's got a good bit of overlap, it's emotionally rather different.
So, what do you think other people ought to know? Any theories about why they haven't learned it already? Any experience with getting someone else to learn something when it started out as your project rather than theirs, especially if the other person was an adult?