I was having something like "The 4 hour workweek" in my mind when I was referring that. You can see this same point in different forms in that book.

Edit: Another tangential stuff is Paul Graham's essay on wealth - http://paulgraham.com/wealth.html. There he specifically mentions that money is not wealth, but something used to move wealth. But the point about there is no fixed wealth and we can always create more wealth, also looks similar to the above mentioned point to me.