Interesting, as far as I seem to remember all the airports in Europe I've been to had this concept, except tiny regional airports. Probably because traditionally pretty much any connecting flight involved transit through a third country that you'd need a separate visa to visit.

The idea is that you "enter the country" when going out from the main part of the airport, but you can go from any arriving flight to any departing flight without doing so, and most of the facilities - shops, waiting rooms, etc - are 'inside the zone' as well.