They could be certainly correlated but why would you assume that growth automatically means an equal (or slightly higher in this case) ridership? After all, the out of towners all didn't take the bus there. Most public transportation I've experienced (subways, buses, trollies, local trains, etc) have a lower-band economic class, for reasons that I could only assume and is an entirely different topic. These lower economic classes aren't pushing the growth of Seattle's population. If Seattle is getting the middle and upper classes to take the bus then they very-well deserve kudos.