Links from books the ultimate authoritative source?

It just occurred to me as I was doing a vanity search that lead to Google Books: wouldn't books be the ultimate authoritative source of links for a search engine?

Books sometimes have full URLs in their footnotes like the example above. They're not links you can click on, but a search engine (like Google) that indexes books can certainly read them.

There are any number of ways of spamming websites that have arbitrary been deemed authoritative, like with form spam. But nobody, to my knowledge, has thought of negotiating links on actual tree flesh in order to get into Google? It would be a very pure source of quality links.