I wonder how many people in the NYC region for whom LGA is convenient actually take connecting flights from LGA to another international gateway as opposed to traveling hours and hours by land to get to JFK so that they can take a nonstop flight to Europe or Asia or S America?

Same thing with people who live or work close to DCA? Would you really take a connecting flight from DCA to EWR, PHL or JFK to get to your long-haul international flight instead of the half-day journey to IAD where you could board a nonstop?

I understand the convenience of LGA and DCA, and the monumental task required over hill and dale to get to JFK or IAD from the cities, respectively, but is it all that common?