In that case (since we are playing with quotes) may I point you to p 142 of that same book, where it says "The calendar should show only the 'hard landscape' around which you do the rest of your actions." and where he goes on to express firmly (in more words than I can quote here) that you should not enter things in your calendar that you would "really like to get done" on that day, only things that "you absolutely have to get done on that day".
But I suppose we interpret things as we please, depending what we ourselves prefer. (I hate subjective planning dates, and always have. I want plain objective facts, that enable me to make correct decisions on the fly.)
bcmyers is correct that DA blames the habit of using daily to-do lists for the tendency to crowd the calendar with things that we merely "want" to do on a particular day. In addition to that, I myself would direct a lot of blame on all the rivaling schools that explicitly tell people to put things on their calendar to be sure they get done. And I would also put some of the blame on DA himself for leaving his text a bit too open for such widely different interpretations.
As for the statistical prevalence of "drowning" I suppose no one here can really know for sure. All I can do is testify that I have heard such complaints many, many times on various forums, and I have heard of all kinds of ugly workarounds for dealing with it. So I think it really is a problem, not for me, not for you, Roger, apparently, but for GTD. Myself, I typically have about 50 next actions (varying between 15 to 150), all clearly defined and without any hesitation. Being a lazy person striving for simplicity, I certainly do not want to have to read all 50 items each and every time that I look at my next list (many times a day) - just to make sure that I am not overlooking something important - that is why I put a red mark on those that I definitely do not want to miss. Yes, bcmyers, that would be an extra layer of complexity for you, but a layer of simplicity for me. It pays off for me because the little time it takes me to put the red mark I easily earn back a thousandfold in terms of reduced time checking the whole list multiple times a day, and in terms of reduced stress. But we are all different.