Cant they teleport? I mean, on a personal basis, without any medium other than a wand neccesary? That would make a mockery of modern immigration theory, much less technique.
The admin is right. The books were never meant to encompass an entire world, with all its complexities and difficulties and exceptions. The author wanted to tell a very specific story about coming of age, struggle and all that jazz. She only developed her world as much as needed to throw a cheap backdrop behind the characters, who are the main focus anyways. And that isnt a bad thing. Those books were heavy enough as it is.... If they had to explain EVERYTHING linked with modern life, even taking magic into account, they would be big enough that you could beat a horse to death with them without too much trouble.
The moral of the story? Go with it. If you run off the edge of the map, you are thinking too hard about it.