It's a good question and one that I have to leave open to someone else to answer as I don't understand the rules on flying through one country and selling tickets through that midway country.
But the difference between AKL-HKG-LHR and AKL-LAX-LHR is 300 miles (nautical or otherwise). While SYD-LAX-LHR is 1000 miles more (than from AKL) and that is in itself 1000 miles longer than going through DXB. So the premium to fly with QF would have to stretch even further I would imagine, due to increased fuel usage. But happy to see some regulars suggest why this could or couldn't happen, perhaps in the morning.
Some years ago it was cheaper to fly United to LHR than to the USA: free side trip to London before or after business in the USA and all those extra points!