@Bogart, i'm not too convinced this may have much relation with the new infrastructure(caffeine) update. But i can't be too sure either.
I agree with your thinking about this update not having a direct relation to caffeine. What I mean is that the new caffeine infrastructure and the rewrite of the Google File System allows Google to do more.
One thing to think about is that caffeine is finding more links and finding them faster. Perhaps, the Halloween Update affects the way PR is passed from the links. It's strange that there hasn't been a PR update for over 210 days.