Rickard made that claim in 1916. Last weekend I started re-reading his classic, Technical Writing. The SU SciTech library has a first edition and a third edition on the shelves.
There's been plenty written about Rickard's little book and it's influence on the field of technical communication. When you remove all of the positivist, constructivist, crapolavist debate, it really is just a finely written little story by a guy who was passionate about concise, clear, and meaningful technical prose. It's the book I want to write someday.
I'll leave you with Rickard's ditty on user-centered techncial writing, or as he puts it, "Remember the reader."
"Somebody must put hard work into every technical article that is written for publication; if not the author, then the editor; if both the author and the editor shirk their duty, the reader will have a headache."