Let's face it: shooting zombies are fun. Maybe it's because we all secretly want to go Postal at some point, and can hide behind the moral mask that these humanoids aren't real humans. There's no moral ambiguity: you have to shoot your former colleague in the head or become zombie chow. There are lots of games tap into our guity pleasures; otherwise games like Resident Evil and Left4Dead wouldn't be so popular. Heck, Capcom basically buit their empire on zombie carcasses.
Everyone needs to be ready for the inevitable zombie apocalypse; even little kids. That's why publisher Destineer has released Little Red Riding Hood's Zombie BBQ.