A dear colleague of mine, Joe Marasco (aka Barbecue Joe) wrote to advise me of another pithy observation on simplicity, this one from the classic Elements of Style:
"Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all his sentences short, or that he avoid all detail and treat his subjects only in outline, but that every word tell."
Speaking of Joe, check out his book, The Software Development Edge: Essays on Managing Successful Projects. Joe is one of the most effective and successful project managers I've had the pleasure of working with, and this book is full of gems from his long career.