I have at least two cents to say about this. I work in publishing, and love acknowledgment sections. They help me find the agents of authors I admire so I can try to acquire similar books (yes, several of my own book contracts have come from acknowledgment sections). So you could say they're a form of career help pay-it-forward.
Besides, I know how much hard work goes into making a book, and lots of people are involved. Especially these days, when books are workshopped, polished, and perfected by many hands. I know that if I were to write a book, I literally wouldn't feel comfortable publishing it without giving a nod to the many, many people without whom the book wouldn't exist in its current form. As a publishing professional, I LOVE being thanked. I have a shelf full of books that have my name in them. I know I'm not the only person who likes being acknowledged. Why not let an author generate goodwill?
He quotes Sarah Nelson usefully:
"It used to be a writer spent 20 years alone in a room," says Sara Nelson, editor of Publishers Weekly, "and came out with an ink-stained manuscript and made a deal with Bennett Cerf. Now it's publishing by committee. Everything's sales and marketing and publicity."
A sad but true tale (don't get me started... the Committee is a topic for a different day). But since that is our world, the world of the publishing Committee, why can't we thank?
One of the thing Jonathan Black comes down hardest on is the style of many Acknowledgments pages, praise he calls "syrupy." Perhaps that's a matter of taste. I LOVE reading acknowledgments section of a book, regardless of whether it was fiction or nonfiction, and particularly when it's goopy and revelatory. I'm a big fan of the cult of author personality--I'm at least as interested in the author as the book, which some people would say is a bad thing, but there it is--and I love to read about what an author things about the people s/he loves. Sometimes I cry when I read them. Yes, it's true.
So anyway. So what if I have ulterior motives? That's only ONE of the points. It's not like a page in the back of a book is bothering anyone. I say, authors, acknowledge away.