I'm going to go back and watch the keynote, but didn't they state otherwise? Changes made on a PC or Mac take 15-20 minutes, no problem. But didn't they demo this happening in seconds?
Quite possibly something cooked up for the demo. They could reduce the interval between syncs. Someone here posted an easy way to cut it to 1 minute, and I'm sure Apple could reduce it even more. But they don't want to do that for everyone all the time because it would clog their servers.