The presence of large corporations is important, but not the only part of the equation. Demographics and location play a role, as do artificially imposed factors such as visa restrictions and whether or not the airport is a hub for a major airline.
For example, over 90 million passengers passed through Atlanta's Hartfield Airport in 2008. Why should Atlanta, wiith a metro population of 5.5 million people have almost 3x the number of passengers as Toronto Pearson? Because Atlanta is Delta's primary connecting hub -- not because there is huge O&D traffic from Atlanta.
Vancouver has more Asian destinations than Seattle because it has a far larger Asian population than Seattle with the business ties and relationships that go along with it (it's not only blue-chip corporate types who travel business class). It is also better known in Asia and most parts of Europe than Seattle -- Starbucks, Boeing and Microsoft notwithstanding -- so tourism is a factor. Finally, it is the only Canadian city on the west coast of North America -- making it Canada's de facto gateway to Asia. Seattle by comparison competes against major airports such as San Francisco and Los Angeles for US traffic. So NO, I don't think it strange at all that Vancouver has more Asian destinations than Seattle. Supporting proof? Seattle has been unable to support a non-stop to Hong Kong, while Vancouver has 3x daily nonstops.
To your point about Portland, yes they DO complain about only having service to Amsterdam and Narita, due partly to history -- Delta tried to build up PDX as an Asian hub. FYI, the Narita route is heavily subsidized by the Port Authority of Portland.
Whatnext, I'm curious about something: Vancouver airport is a huge employment and tax generator for the Lower Mainland in the same way you argue that Air Canada is. So why denigrate Trofiren's hope of seeing YVR develop into a leading North American transit hub for Asian traffic?