Apparently there is a free carpark somewhere at Stansted that allows an hour's free parking and offers a bus service to and from the terminal. So by the time you have caught the bus and reached the terminal you have to catch another bus back fairly smartly in order not to exceed the hour's free parking, so you pretty much have to use the two quid drop off zone. Heathrow and Gatwick seem to be two of the very few airports that allow free set down and pick up. But I guess they have studied the idea of pay barriers and realised that if they were instituted for Heathrow Terminals 1 to 3 the entire airport would gridlock to a halt.