Pop culture = a mirror for a society's hopes and fears + social fads of the time. I vaguely remember as a young kid of the '80s that there were post-apocalyptic media around very commonly, often having to do with a fictional ending to the real-life nuclear threat. Now our main threat is economic, something hard to understand, assess, and predict; ultimately self-destructive. There are even financial institutions given the zombie title, for they are dead on the inside but continue to exhibit symptoms of life. There is no "us vs them" like in the cold war - rather the fear is that the downfall will be internal, that the "us" will turn on one another.
Heck, it could even be a political reflection. You either have to be parroting Ed Schulz or Bill O'Reilly, not in between. In that way, the divisive automaton nature of the political discourse in this country is also a little reminiscent of a late night zombie flick.