Looks like Rockstar thought of that. According to an email many readers have received from Rockstar in the States, the game is "region locked for [its]specific territories". Which consoles this includes and whether it applies to the multiplayer we're not sure.
The email goes on to reinforce Rockstar Oz's earlier statement regarding the changes to our version of the game being minor. Kotaku AU's attempts to get an answer from Rockstar Oz regarding the region locking have been met with failure, but this looks official to me.