I'd be inclined to agree with Jamie. Furthermore, routes to the East Coast or generally the East side of the US are closer and hence less hungry in terms of ac tied up. A West coast service can see an A330 gone for 24 hours, while a NYC or even Toronto is a lot shorter allowing for potentially greater utilisation of said fleet and if more passengers can be carried on said services it is not just revenue from tickets, the ancillary revenues are greater.