But only CX flies to the United States, including two flights a day to Anchorage, I believe. (Vancouver, Toronto, SF, LA, and NYC being the other NAmerican gateways)

Also, considering CX's other partners include
Qantas, BA, and AA, so the overlap makes sense from that angle too...

And, fwiw, I notice CX flies to Australia/NZ via Hong Kong. Though I'd be (pleasantly) surprised if AS set the partner redemption limits to be more equivalent to what you say is avail on *.