I mean Arlington and Alexandria both heavily use their bus systems as feeder networks to their respective Metro stations. Fairfax Connector as well, to a certain extent. Not sure what Loudoun is up to with its bus fleet - I only know of their commuter coach buses.

The fact is that the further you get from the core of the region, the more that park-and-ride stations make sense. It's not very cost effective to run low-ridership buses, when you can instead build a parking garage to absorb riders arriving by automobile. That's why stations like Franconia-Springfield and Vienna make sense to have large garages. By contrast, the small paid lot at Braddock Road never made any sense to me.