I'm equally confused here. Who searches "Seth Godin The Knot" and if the first result isn't that exact book, goes and buys a book about knots or weddings or something? The book should be there in plain view at the top of organic best matches. Did they really test this "yield" claim?

Sophisticated advertisers measure “incrementality”, which is exactly what you’re talking about. Alas, most advertisers are not sophisticated.