I'll not respond too far on your comment, simply because it's pulling the thread off topic.
I will say that the general public (that would be more than 50% of the population) does not have a better than sixth grade vocabulary. They actually teach you to write with a sixth grade vocabulary in business and communications because of that.
I'm bragging, but it's also truth: I have a better vocabulary than 99% of the people I meet. I read 3-5 books a week, on average--both fiction and non-fiction. I seldom come across a word I do not understand, because I either know the word, can break the word into root components, or I can derive the meaning from context.
I also test at the genius level on IQ tests.
And I have misunderstood emails, posts on message boards, and other forms of written communication, simply because I did not know the sender well enough to intuit the tone of the message.
It has nothing to do with intelligence or vocabulary. It has everything to do with the fact that humans communicate primarily with speech, and have adjusted their receptors accordingly.