As a former primary teacher and recovered dyslexic, I'm not at all surprised that 40% of the population are only up to a 5th grade level (if that).
I'm a fluent adult, and there are some articles in the wikipedia that leave me going 'huh?!' because they're too complex and convoluted... I think a really good writer who knows what they're talking about can make complicated information seem simple, but a poor writer or someone overly involved in the subject can make the simple seem incredibly complex because they assume that everyone else has a certain level of understanding that they don't actually have.