@ Buffer Overflow:
"5) Even happens when the iPad user is in a different domain. This is, IMO, proof positive that it is an Exchange problem (as well). No one from a different domain should ever be able to cause an appointment in an organiser's mailbox to be deleted; yet that is exactly what is happening to us."
What do you mean by "happens when the iPad user in in a different domain"? Do you mean that someone in a different domain sends a meeting request that is then "Adjusted" on the iOS device of a user in a different domain? If so, I don't see how it is much different than being in the same domain; the entry on Dave's calendar from Company A is the original but was sent to Joe at Company B. Joe accepts the meeting (whether by his own hand or by his delegate) then later his iOS device "Updates" the appointment to mark him as the organizer and may or may not send a cancellation to Dave and/or other attendees.
The issue is not that Exchange has a bug, but rather the problem is in Apple's implementation of ActiveSync. Sure, Exchange could act as a "Gatekeeper" and deny this type of erroneous update, which would be a very helpful thing to mitigate these issues before they occur, but as long as EAS is implemented properly there should be no need for this.