The "original" (in the non-Vodoo sense) zombies shown in George Romero's "living dead" movies made no claims that the undead were scientifically explainable -- it was later movies like 28 Days Later that tried to rationalize them as infected, living people, to their detriment, I think.
In 28 Days Later the infected starve to death, I can't remember them being overly supernatural.
It is The Walking Dead in which the zombies are basically immortal but useless. Unless the plot requires otherwise. After Season 1 it is a terribly written show. Don't get me started.
28 Days Later is scarier because the infected, living humans can chase you down, climb and open doors, and the infection spreads much faster. I always wondered what The Walking Dead would have been like if the survivors couldn't clear out a prison full of zombies with hand to hand weapons. 28 Years Later is coming out this year, and they going to show what happens to humanity stuck in the UK that's been overrun by the Rage virus and presumably quarantined all this time by the rest of the world.
To me that makes it more boring though. The interesting part about the Romero movies is that the survivors underestimate both the zombies and their fellow survivors. They think because they can deal with individual zombies that they are safe. But they forget that zombies in mass are dangerous and that even more than that, their fellow survivors might be not be friendly.
