[xsmasher]

I could speculate wildly. Zombie films play on fear of death/disease, and the fear of someone you know trying to kill you -- or you having to kill them. I don't see anything peculiarly American about those themes though; I'd imagine they're pretty universal.

Zombies also represent the fear of something that looks almost human, but is not, and which outnumber you. That resonates with xenophobia (we're outnumbered, they're not human, and they work for $3 a day!) or pure selfish narcissism (I am the only "real" person, everyone else is an automaton / homunculus.)

There are also market forces at play - you can shoot dozens of them in the head and still get a "teen" rating for your movie or video game.

I'd love to hear other theories.

EDIT: Thought of another one. The "zombie apocalypse" shows the breakdown of civilization, and makes us realize that it's only goodwill that keeps society running. Our picture windows, screen doors, and windshields are only "polite" barriers that anyone could break through in an instant if they discarded civilized values. Maybe we (America) fear the end of empire, and are obsessed with what it might look like?