In recent trends I know that airlines will provide competitive fare for passengers flying from another airlines hub to connect to connect through their hubs. I fly like this way do you think I already got a competitive fare?

Hub Owner's route:
NW DTW-NRT-HKG (DTW and NRT are NW's Hub)
Competitior:
AA DTW-ORD-NRT, connect another airline NRT-HKG (ORD is AA's Hub)

The price I paid is around US$200 less for AA than NW.

The Strange Fact I discovered:
Normally for HKG-US R/T, ticketing and originating in US is CHEAPER than at HKG, but I found an ad in HK that HKG-Toronto-HKG(via ORD, AA) is US$2xx cheaper than my AA DTW-HKG-DTW. Why this? That means HKG have cheaper ticketing now or the HKG-Toronto route have more competition than HKG-DTW?

Thanks