In reference to the VS flights to SYD, i know its a sod to get seats on, as i work for a well know travel firm in the UK and we sell a lot of seats on VS and we can very rarely get seats on the SYD flight, now i know the LHR - HKG flight is busy, but we have problems with the HKG-SYD route too.
Just cause seats are hard to get does not mean it has a good yield.