Economics of Contempt

Speaking of David Wessel's book, In Fed We Trust, how does everyone have advance copies? The release date is August 4th, but several bloggers have apparently read it, or at least have it, already. Tyler Cowen has already read it and recommended it; Ezra Klein says he has it "on the nightstand at home"; and Arnold Kling has already skimmed it (and dismissed it for containing too many pesky facts about what actually happened). I understand that publishers send advance copies to journalists to try to get them to write a review, but neither Cowen nor Kling is a journalist. I practically keep the publishers in business with how many books I buy—plus, I always buy the hardcover version, and often the ebook version as well (I like to be able to search books that I've read). But in my entire life, I've never once been offered an advance copy of a book. What gives?