This is the point that I think is completely lost on the author of the article, probably because of a focus on API design. It's a good thing that we can replace that dog-eared copy of Moby Dick with a shiny new one when the time comes, and our users don't need to change their URLs.
APIs are intended to be used primarily by machines, so it's fine for the URL structure to preference the predictable uniqueness of ids. However, for most URLs intended for use by humans, the forces are different.
A human-readable URL is not a pointer, it's a symlink.