When I was in high school, I was one of the top English students. I started attending the KH in my sophomore year. The congregtion I attended was comprised of much better educated people than average dubs. It was in the most exclusive part of town. I did not live in that part of town, but the people who studied with me did. I never found any grammatical or spelling errors in any Watchtower literature, but it was written on about a fifth-grade level. Even in that congregation there were some who could use the English language about as well as an elementary school pupil.
When I moved to other locations, the language skills of the dubs were, overall, much worse. It was obvious that some of the men could not really understand the talk outlines and would interpret them in strange ways. The readers at the Watchtower study would mispronounce common words. The elder that I married was semi-literate at best, but still felt he was given to me by Jehovah to explain the world and everything else to me.
To be fair, I have met a lot of non-JW's who were just as handicapped with language skills. I have worked with many people and attended college classes with many people who did not understand when to use an apostrophe, or understand what a run-on sentence or a fragment was.
Surely it's easier to deceive people who don't understand the nuances of language, so JW's have an advantage with such people and draw them in.