Here is one of the best examples of clear communication I know:

http://norvig.com/spell-correct.html

Norvig is a genius, and his genius is reflected in how he can so succinctly and clearly explain how to write a spell checker, without falling into elaborate jargon or droning on without getting to the point.

And that goes equally for his code and his prose, by the way.

There are many people who use a lot more jargon and verbosity to make their points, who are not in the same league as Norvig in terms of intelligence.

A classical joke from the GDR (about scientific language, not about farmers):

"The production volume of agriculturists is the reciprocal of the intellectual capacity of the producers."

also known as:

"The less intelligent the farmer, the bigger his potatoes."