It appears that events that are part of a recurring
appointment, but have modified attributes (date change
or location change, etc) are not exported.
Outlook keeps these as part of the recurring
appointment - but they are stored as 'exceptions' to the
IAppointment object.
Outlook's native iCalendar export also misses this.
Attached is a sample Outlook MSG file generated by
Outlook 2000 - is contains a single recurring
appointment (every 2nd monday from 1/2003) with one
exception (meeting moved to tuesday 11th of february -
and retitled 'cancelled')
Apple's iCal software appears to handle this (or at least
I've received ics files generated by iCal that are correct) -
and the RFC appears to support this.