SEA is in such an out-of the-way location that the only way it works as a hub is for either an Alaskan/US hub or for a Pacific Rim hub, which it is. The SEA market has traditionally been a strong O&D area with the strong marine and timber industries in that part of the country. Alaska Airlines has been strong in SEA for many years now, and it made sense for SEA to become their primary hub. Also remember that they've got a strong hub-like presence in PDX and the Bay Area.
As far as Mexico goes, it's not really a 'novelty' for them. They've got quite a number of routes down there, and multiple flights per day on those routes. The stricken flight 183(?) was a PVR-SFO flight.
I can't quote SEA's current international route system, but in years past, they've supported an SAS daily flight, numerous NWA Pacific Rim flights, I recall Thai at SEA, China Eastern, etc., so the demand is there.
I also wouldn't say that AS tricks people into an SEA connection. The only possibility for that might be the flights to the East Coast from either SoCal or Arizona. As for flights within the Pacific Northwest, they've got enough direct flights, and good enough connections at PDX and the Bay Area to cover that.
Alaska is a bigger player in the western US that people give them credit for. They've done their homework when it comes to airline and route expansion. And SEA is one of the more entertaining airports to spot at, plus that part of the country is just flat gorgeous.
Tom in NO (at MSY)
"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina