Wfnz: 

 

Ok this makes some sense as to why I have to go with the more expensive for less data rural plan.

What's to stop me ordering a non rural SIM/Plan to another address and using it here?

Fair use and the fact that they could end the service because you're not using it for a personal mobile device(quoting voda's terms)

https://www.vodafone.co.nz/legal/terms-conditions/pay-monthly/