How would that work? Countries don't have radar coverage over the entire ocean. Even if the aircraft were noticed, which country would be responsible for upholding the international accords? If Russian aircraft were scrambling to stop hobbiest aircraft off the coast of Alaska, that would be a political nightmare.
Given the time involved in gaining a pilots license and cost of aircraft, it seems that the adage 'Caveat Emptor' works just fine for oceanic air crossings.