@Andrew Nacin -

By the way: is there any documentation on how the various transients work together, including how often WordPress checks for updates, whether or not api.wordpress.org sends the update, and when/how often the update routine executes?

Right now, I'm sitting here with an update_core object that has had the 3.7.1 update (since last evening sometime), but the automatic update isn't firing. That's being controlled by the delayed rollout, but I can't seem to track down how all that works together.