It IS the IP adress that prevents downloading because the WiFi or 3G has to go throught the local comunication protocol to identify itself. Cosequently the supplier computer knows exactly where the receving unit is! It is sorta like the phone caller ID.
I just checked Amazon and this is what is on their website:
Belize We are excited to now ship Kindle to Belize. Customers in Belize will enjoy:
Download Books Instantly: You can download books to your computer and transfer them to your Kindle via USB. Kindle wireless is not currently available in your country.