I would imagine that if we stepped back and looked at dc as a whole we would find that lots of foreigners are buying influence and favors there. The smart ones use a dc law/lobby firm as a cut out, but at over $1K per hour that probably limits the players to the really rich ones like asian business types, euro merchant bankers, and saudi princes. Your costs are lower if good marketing people can tie your influence to something big media likes, like climate change.
You very well may be right. But, the smart ones don't get caught. Any previous case is just as bad as this one, but if we don't know about it, we don't know about it.