Not all of Alaska's flights to Boston go directly to Seattle, we've gone to Minneapolis a few times then on to Beantown. I think it all depends on what time your flying. Flights coming back from Beantown don't always go through Seattle either, we've had flights stop in Detroit, then Minneapolis then on to Anchorage. Our flight this summer will go through Seattle but it's just a stop and we don't change planes.
I have never seen a direct flight on Alaska Airlines to the east coast or vice versa.
