Sometimes I leave a suggestion for improvement, but I won't usually say the same thing someone else just said. Say someone left a lot out of a review, and someone already commented and made the suggestions I was going to make. We were told about a year ago, that repeatedly saying the same thing to one person was "not cool."
So, I usually only offer a suggestion on a vote below "useful" if I'm the first one to comment.
If NO ONE votes on poor reviews, the only votes they will get are from people who always vote EU for everything and that reviewer will never learn to accept creative criticism and continue to write poor reviews. Don't you think? I DO vote on reviews that are less than "useful" but I don't feel the need to always leave a comment. If the reviewer has read even half a dozen EU reviews, I think most would see the difference between 3 poorly written paragraphs and a truly EU review.