I read Chuck Klosterman's incredible take on the zombie phenomenon as well as their staying power.
He argues that killing zombies isn't all that much different than other mondane tasks. The fear and danger of a zombie attack isn't that they are individually frightening - but the sheer number of them is insurmountable. Fighting through a zombie attack is like filling out time sheets or working on an assembly line. Zombies are like Mondays - to put it in terms that people with unoriginal Facebook statuses can understand.
But I think their appeal goes further than that:
Anyone can kill a zombie.
They are slow and stupid and uncoordinated. Like that first kid that hits puberty in junior high. It isn't like X-Men or Superman or any other movie about fighting evil. You don't have to pretend to be someone else. Zombie movies allow you to pretend to be yourself - but the cocky, arrogant version you see in your head.
Everyone talks a tough game when they read a news story. "Dude - if I was in that bank when it was getting robbed I totally would have beaten the crap out of those 17 guys with machine guns and saved everyone." You know you do it. I do it - in my head I could have stopped JFK's assasination, the Civil War and the extinction of dinosaurs. With nothing but a beard and a smile.
The zombie apocolypse is just like any of those situations. Strong people think about how they'd be able to kill zombies, smart people imagine the plan they would put together, and slutty girls at bars who's only skill is flirting with guys for free drinks would finally get wiped out.
It is like the opposite of Lord of the Rings - instead of making the hero a loser that we can identify with - the hero is you - which, in most cases, is also a loser.
So Klosterman is right - fighting the zombie apocolypse is much like our fight with everyday life. But it allows us to imagine going through that fight as the person we are (or want to be) in our head - not the one that agrees to work weekends or refuses to send back a bad meal or helps that guy you don't like move his couch because you can't say no.
Because in the zombie apocolypse - you get to bash that guy's head in.