Little fish may not matter matter on their own, but if the big fish follow the little fish (even unconsciously) then feeding the little fish is a good strategy for subtly influencing the big fish.
So while his motivation may be different than most authors, the path he must follow to make the book do well is largely the same. We'll likely see more things you wouldn't expect to see him do. A billionaire's ego is on the line.
You can see a transcript of a conversation I had with him here: http://www.cnet.com/news/talking-tech-with-peter-thiel-inves...
Every sentence he said (as well as his responses in the AMA) was a a complete idea, full of insight and depth. Mere mortals, like yours truly, need to take a couple minutes to process examples and counterexamples, to define the assumptions made, to wonder at the implications. You want him to speak more on the subject.
Instead, it's so obvious to him that he continues speaking and you've just missed 3 more profound statements. Makes him fascinating to listen to.
I don't think most famous people need the karma bad enough to even set aside that much time.