The one weird thing is that they charge the same for data traffic that's local to NZ. That may be just because it's hard to explain to users why some bits cost more than others.
Used to be done that way some years back, but gradually the ISPs gave up on it. I think a large part of the reason is that it's hard to look at an address and say for sure whether it's in NZ or not without a human giving it the once over.