I believe we are indeed cyrodiilic vampires simply for our ability to walk amongst people. Was it not the cyrodiilic that made a deal with vile to be granted their sanity and a control of the thirst?
I did always wonder how much blood did a vampire need to drink to be "full". In Oblivion and Skyrim, not much. Yet in Skyrim we see piles of bodies in vampire caves, and pieces of human bodies and organs on plates.
