A regular-routed version of the service could conveninetly connect the big station with hubs of local transportation, parking lots and other "recruiting" points.
But the airport shuttles ... which are often private commercial operations ... do underline the fact that Americans get out of their cars to get on a plane, making it one transport task that allows us to sidestep the hegemony of the car. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.