Here's something to pick our collective spirits up:
According to Google's infallible algorithms, 20% of the content on LessWrong.com falls within the 'Advanced' reading level. For comparison, another well-known bastion of intelligence on the internets, Hacker News, only has 4% of it's content in that category.
Strangely, inserting a space before the name of the site in the query tends to reduce the amount of content that falls in the highest bucket, but I am told that highly trained Google engineers are interrogating the bug in a dimly lit room as we speak, and expect it to crack soon.
Yes. In an ideal world everything interesting and important would be comprehensible to a ten-year-old. But since we don't live in an ideal world and many interesting and important ideas require difficult concepts and complex vocabulary we can be pleased with this evidence that we are rather unique in our ability and propensity to talk about important, difficult ideas.
It's not evidence of any such thing. Read Orwell's Politics And The English Language - http://www.mtholyoke.edu/acad/intrel/orwell46.htm . Every example of bad writing he gives there would show up as 'advanced'.