Found this on AS website, quite interesting.
Reversal of Baggage Rule Changes - Separate Ticket Itinerary
** UPDATE January 17, 2013 **
Alaska Airlines has reversed a recent policy change that would have restricted the ability to check to a final destination when separate tickets are presented at check-in for international travel.
While we recommend traveling on one ticket, we recognize this isn't always possible, and Alaska Airlines will continue to check baggage to our customers’ final destinations when separate tickets are presented.
When travelling internationally across multiple tickets, the international carrier's rules and fees will apply. When traveling within the U.S., the baggage rules and fees of the ticket being used at the location of bag-check will apply.