A reasonable inference. Yahoo's service, like many, is not true push, but a timed server sniff, called "pull" for lack of a better term. I was under the impression that BB represented a true server-sided push service.If you watch the keynote carefuly he did say "the iPhone will sync with your calendar and contacts on MAC AND Windows". Windows doesn't really have any other calendar programs that are worth mentioning other than outlook.
Email can be synced too, but only via IMAP (possibly iTunes too). IMAP will sync all your folders etc, but is not push in anyway. Although Yahoo! managed to make it push somehow (probably sends a text message when you have new email, forcing the phone to go pick it up. Much like the blackberries, OTA ActiveSync works behind the curtains).