The answer is more cut and dry. First off, without discussing taming at all, the humidity and heat requirements needed to maintain survival cannot safely exist in a human household. This excludes them from free-roaming successfully, and from becoming "household pets".
It's no coincidence that the book authors' own Savannah Monitors are some of the most fat and dehydrated animals I've seen on the Internet.
Secondly, here's a quick glance at the Wikipedia page for "Domestication":
http://en.wikipedia.org/wiki/Domestication
One of the main characteristics of domestication (which Wikipedia coincidentally calls "taming") is that the animal is bred under human control. Since over 99% of Savannah Monitors are wild caught, wild impregnated and bred, and imported, this completely excludes the Savannah Monitor from qualifying as a domesticated animal.
Monitors are wild animals. Though we sometimes take them into our homes, and sometimes have success in getting them to not bite our faces off, they are still wild animals. They will never be dogs.