Especially that they launched US-only (?), but the whole world is playing anyway thanks to game's APK being spread on-line. I'm writing this from Poland, coming straight from 2 hours walk from work, catching Pokemon and leveling up on the way :).
It first launched in Australia, and is available in a few countries right now (Australia/New Zealand/USA). I believe the rollout to the UK/Asia/other countries is on hold due to issues with the huge volume of traffic overwhelming Niantic's servers.
Seems like this would be very easy for them to block since they know your GPS coordinates. They could just pop up a message saying "Pokemon Go is not yet available in your region," although, the good will demonstrated by allowing customers in other countries to play would probably be better than arbitrarily blocking them.
They could. If they did, they'd probably kill the game on the spot, or at least significantly curtail its popularity. As it is right now, the game is a global phenomenon, and it's getting immensely popular worldwide.
