Like any business, QF charge what they can get away with in each location; they aren't a co-op for the good of the people.
The supermarkets charge more in the rich end of town because they can; landlords charge as much rent as they can without the tenants squealing too much or walking; it's cheaper for a Kiwi to book a flight from Australia to New Zealand using the Australian website; it's not price gouging – it's just market forces, IMHO.