I know you are saying so at least partially in jest, but the comment does illustrate a very common and IMO annoying trend - the demystification of the supernatural. So many stories, games, books, etc. seem to want to explain away all the fantasy.
Sure vampires don't have what it takes to keep from freezing, biologically speaking, but they do have supernatural powers that can let them turn into mist, bast, wolves, shadows, change their shape, invade the minds and dreams of their victims. I am pretty sure that they could keep from freezing..
