What about the rise in humidity when in recirculate mode? If the car is moving it could presumably cool the interior using a radiator like the engine itself is cooled. If you're in recirculate mode though the humidity will rise and you need to activate the compressor.

My '02 Civic has a humidity sensor in the cabin so I've always assumed it could switch the compressor on/off based on that as well as the cooling.

Edit:I should add that my '02 Civic has climate control so presumably it can be more clever in where it gets cold air for the cabin. If it cool it enough without using the compressor perhaps it will do so?