Why?
They are merely booksellers...
Elsie, see my previous post on why. An academic or scientific bookseller's reputation is their life.
When someone, like js1138, says show me something that has been peer-reviewed or in a textbook on this topic, the whole implicit argument is that there is a much higher level of scientific credibility presumed in those regards vs. something posted, say, on a website or in a popular magazine. Why is that?
Journal and book publishers work very hard at building the highest reputation possible by being as selective as possible so they can be as prestigious as possible, such that when something is published with their name on it, that carries weight. Gravitas, if you will.
When I buy a Wiley book, or an O'Reilly software book, it's because I don't want to have to start from square one independently verifying the author's credibility on the subject in question; I am paying for someone else to have done that. If Wiley is no different from HarperCollins, if I'm getting Harry Potter and the History of Evolutionary Dogmatism, instead of a serious scientific text, it's no use to me. Unless I'm looking for entertainment.
Hope that makes sense.