You are right about that. I suppose I was just speculating on why the author was including <strong> as a no no. That the thought of "I am 'stronging' this text" didn't indicate significance to him while "I am 'emphasizing' this text" related significance to him. In which case, <strong> would seem like just another name for <bold> while not denoting importance.

I myself did not clearly understand that <strong> was actually more "powerful" than <em>. I appreciate you clearly stating the relationship between <strong> and <em>.