Did youy ever get any help with this? I have the iPhone 4 and have been using the calendar and it is synced with icloud - at least it tells me it is. I just an iPad 3rd gen and everything synced except for the calendar.
Go to Settings->Mail,Contacts,Calendars and scroll down to Calendar. For both iPhone and iPad, make sure that the default calendar is NOT "Calendar" but is the same one of those listed under iCloud, preferably "Home". (and of course follow the other advice on functions that are "on".