1) It happens with Android devices as well
2) The more meeting attendees, the more likely it will happen
3) Recurring meetings more likely than single ones (but can be either)
4) There is a KB article for Exchange 2007 (2521063), but none for 2010
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.
I would like to believe that Exchange 2010 SP1 RU 7v2 or Exchange 2010 SP2 RU 4v2 will fix the problem, however I have yet to see any indication that this is even acknowledged as an Exchange problem.