Since airplanes began to carry passengers, there have been high and low seasons which correspond with travel patterns and vacation periods. For Europe and Asia, the high season runs through the Northern Hemisphere summer (and vice versa in the Southern Hemisphere). For the Caribbean/Mexico and south, the high season has been the winter. There is nothing wrong with a company/industry attempting to extract the maximum dollar from a scarce product when demand is highest. If you want to travel when others also want to travel, and there are a limited number of seats on sale, then you should be prepared to pay a premium. If a kid, as you put it, (or his parents) can afford to go to school in Canada, they can afford the air fare to get back home. S/he doesn't need AC (or CX) to subsidize his or her return travel!

I think it is wrong to base your perception on the trough instead of the peak. Your $900 fare is based on a period of low demand and surplus inventory, and thus the fare is indeed lower. But the norm is closer to a midway point between the high fare of $1500 and the lower fare...likely in the $1200 to $1300 range. (My sweet point is about $1000 a/i for destinations in China and I have flexibility in when I want to travel there.)

It's not that you can't get to HKG by any other means. There are two nonstop carriers offering a half dozen flights a day from Canada, and dozens of other carriers that will get you there with a single connection, so competition is also a factor in pricing but there are competing demands too on the competition.