Perhaps because you are reading an article in O'Reilly's website, whom sells David Flanagan. That out of the way, I thinkn he's entitled to a little self promotion at any point in the article since this is the man behind such gems as JavaScript: The Definitive Guide, and The Ruby Programing Language.
He is trying to sell you stuff, but honestly you should go right ahead and buy what he's advertising because his books are really that good.
Yeah I noticed it too late to edit the post. I'm on the 30th hour of a coding marathon and I'm starting to feel my neurons burning up and leaving me numb as hell. You can easily spot places where my train of thought kind of crashed into a wall. Oh well, c'est la vie.
He is trying to sell you stuff, but honestly you should go right ahead and buy what he's advertising because his books are really that good.