To some extent you are right. And I deal with this question in the book: why write a book if these techniques work? I'll leave my answer for the book readers.
That said, then there's the question why read any books about trading? And to that I have to say, why not read every book about trading? Or at least the the ones that go through some kind of peer filter and you can say they are probably pretty decent. When I want to master a field I try to read every book about the history of that field, biographies, interviews, books and articles about techniques and the history of those techniqes. In trading, everything from Edwin Lefevres early books (not just Reminiscences but "The Making of a Stockbroker" and others) to Graham's stuff to Adam Smith, Schwager, Crabel, Connors, etc etc etc.
When I was a kid I was taking lessons from the then US chess champion. I arrived at his house once and he was reading a total "basics of chess" book, and going through one of the games. We spent the whole lesson giong through the commentary in the book. His point was that he tried to learn from every chess book possible. And that if all he did was play chess and never study it he would never succeed at it.
Anyway, I hope people enjoy the book. In this game, if you learn one thing then hopefully that can directly transfer into paying for it.
-James