Not sure as to when the requlation took affect, but I beleive the reasoning was to prevent foreign flights to be in competition with domestic services. Many international flights make stops in several countries but do not make more than one stop per country. My son makes many flights to Canada but must return to the US before going back to Canada. He flies from Chicago O'Hare to Toronto, Ontario, and other places in Canada but each time must return to a US destination. He goes through many passport pages in a month!