everything is measurable, if you can't measure it, don't do it.
>on technology that changes on a monthly basis?
if you don't have a model of how SEO works, you can not improve on this model, even with new information. that books provides a - sustainable, working, applicable, employable - model.
>That's the reason nobody reads books on SEO. It's the same for web development.
Search Engine Marketing Incorporated
http://www.amazon.com/Search-Engine-Marketing-Inc-Companys/d... [not an affiliate link]
sadly, nobody ever does.