Yes, it's things like these that I find bizarre.

In the meantime, I read the chapters of Anderegg's book you cited above. I find his thesis very interesting, but as always in the history of ideas, it's hard to estimate the relative significance of particular cultural tropes, especially since I know little about all the other factors that could have influenced the development of this characteristic modern American stereotype. I've put his book on my reading list, so I'll probably have more comments when I get to reading it.