Needless fluff sections on philately basics. Leave that stuff on the website.
I don't have a copy of the book to see how much space they devote to such "fluff", but keep in mind what is fluff to you might be new and interesting information to someone else. There are undoubtedly many beginners or casual collectors who buy that book, and for some of them it might be their introduction to collecting. Keep in mind the USPS is writing it for the "intelligent but uninformed reader", so to speak, and not for advanced collectors. Even Scott devotes a fair amount of pages to what could be considered "basics" in the into to their catalogues.