My point is that it's not clear whether the following query would match that VEVENT or not:
SELECT * FROM VEVENT WHERE ATTENDEE = "foo@xxxxxxxxxxx" AND PARAM(ATTENDEE, PARTSTAT) = ACCEPTED
You see the VEVENT contains an ATTENDEE whose value matches "foo@xxxxxxxxxxx", and an ATTENDEE whose PARTSTAT matches "ACCEPTED", so it would be considered a match if each time the ATTENDEE property was used, it was taken to mean "any ATTENDEE of the VEVENT".
BEGIN:VEVENT [...] ATTENDEE;PARTSTAT=NEEDS-ACTION:foo@xxxxxxxxxxx ATTENDEE;PARTSTAT=ACCEPTED:bar@xxxxxxxxxxx END:VEVENT
When would you ever want it to match a value of one property, and parameter of another property for the same property name?