That is great werepossum!
The T-virus thing sounds almost like a plausible reason but it overlooks the fact that the human digestive tract is not directly connect to all body parts, especially the brain. It the circulatory system is down, then there is no efficient manner to get the energy from the food to the brain. Other than that, a very good explanation of how a virus works.
As for trying to research any of the events in the Zombie Survival Guide, especially on the internet, if it is not coming from a reliable source, ie official news, police, governmental, or hospital records, it is most likely been fabricated by some fan. The internet has a horrible habit of lying to people

If you stumble upon something that you feel is truly an example or proof of this fetish(merely meaning a fanatical love of or desire for, not always sexual) check the creation date. If it was made any time after the release of the book, probably not a reliable source.
Simply because something is imaginable does not make it possible. I imagine lincoln coming back to life and fighting Osama Bin Laden in a cage fight. Imaginable, not possible. Absolute statements are null and void if any exclusion can be found or a part of it can be proven false.
Yes, a body can mutate and change its needs, Antisanta, but what we are discussing here is not a mutation so much as a complete biological overhaul. Lets use my trusty "out-of-context-machine" to throw some perspective on this. I have a 1988 Lincoln TC. It runs on gas, is air cooled, and has a radio that has all the static channels you could want. I decide one day to make it run independent of air and gas and instead take its energy from nuclear fusion in the trunk. It just ain't gonna happen, much to the same degree that a human body cannot be independent of O2, food, and water but still function to any degree. The time it would take to convert every cell, even 10% of the cells to such a state every other cell would have rotted, shriveled, and blown away as dust in the wind, all we are is dust in the wind.(Sorry, love that song.)
The idea of undeath has been around for as long as death, and therefore man, because man inherently fears the unknown. He cannot grasp the fact that eventually he will be as important as, well, dust in the wind. Death is a massive change and nobody can know what truly awaits you once you kick it. Zombies, ghosts, vampires, etc. are all "security blankets" for man, giving him the slight hope that he either won't die, or something happens to you after you die than simply rotting in a box. Psychology and human nature are the reason zombies "exist", not viruses or magic.
Ignorance is a two way street, Scarlet. All the trivial knowledge in the world won't protect you if you are ignorant to basic needs of man and how to fulfill those needs. That holds true in any situation, whether it is your zombie holocaust or something as mundane as having to survive you 9-5 life.
Kiltman
P.S. God, my posts are long. I'll work on that...