Do the calendars sync to something via your PC or on the Internet?
Both my ipad and iphone sync calendars to my work Exchange server and also to my gmail account (use the Exchange interface) and sync OTA essentially real-time. The two different calendars (work and gmail) show as different colors.
If you use neither of these, then syncing to ical on OSX should be fine, but it would only update when synced with itunes. Not sure what calendars other than Outlook iTunes on PC syncs to.