I also find that they evolve. Like if you watch 5 keynotes that he's done in the same week, or even the same month, it's the same spiel. Even when he does Q&A, he usually goes off on a tangeant that ignores the question and gets what he's trying to say out... sometimes he doesn't even let them finish the question (although he's become a LOT better at answering the question and engaging with the fan, lately)

BUT, if you stack up his keynotes over time, you'll see there's an evolution of thought process, and you can see where his attention is currently being given.