As I understand it he envisions that somehow the tweets also feed into the book, so that you can have the tweets and discussions on the Kindle while reading the book.
And seeing what others have marked in a book only works for amazon's books, so maybe he hasn't seen that feature.
And personally I don't like the tweet function on the Kindle at all!
I want people to see the quote (as long as possible) and a short link to the full quote with book and my comment. But instead I get some tweet that looks like I've been hacked. Looks horrible!
Hope they change this or make it customizable in the future (or even a hack that allows me to change the format).