Trivia: The writers of Shaun of the Dead are in this film as a cameo. They are the zombies in the photo booth (around the time when Riley is in the gambling pit run by the midget).
Trivia: Tom Savini plays the "machete zombie." This is a callback to the original Dawn of the Dead (1978) where he played the living version of that character- a motorcycle riding hillbilly. He also did special makeup effects on Dawn and Day of the Dead (1985).
Trivia: Robert Joy, who plays Charlie, was in Amityville 3-D. When one of the monsters came out of the well in that movie, it blew fire on him and burned half of his face, the same half that was burned in this movie.
Answer: Riley feels that they have just the right to be there as the living do. Besides, those zombies survived all the missles and are coming to the city while Riley and the gang are leaving. So why waste the ammunition?
Jason Riley