Many of the comments on this page show why Rich gave the keynote. Because the same advantages of type checking are put forward as a reason to not use clojure over and over. They're not wrong, static typing has advantages, but I see little acceptance of any tradeoffs (or even acceptance that such tradeoffs exist: concretion of information, coupling of distant components by shared types etc etc etc I'm just paraphrasing the keynote).
He was highlighting the value proposition and tradeoffs of: being data-oriented, being dynamic and clojure.spec niceness. He felt the need to do this because he clearly felt that some people who were wavering about clojure were unsure why it was dynamic: "can't we have all this great stuff AND static types". He wanted to say "yes quite possibly you could, BUT here's the reasons why I didn't add types".