Yeah, there are plenty of reasons why a zombie apocalypse would fail before it ever got started in America. Way too many gun owners in the United States and things are too spread out in the midwest and definitely in the southwest for a zombie plague to ever spread by dead people on foot. Also, the one thing that zombie movies never take into account is that human teeth are incapable of biting through cloth. Not even healthy human teeth can bite through a t-shirt; so dead, rotten teeth have even less of a chance.
After several failed attempts to bite through blue jeans, leather jackets, business suits, etc. you'd have a bunch of toothless, harmless zombies roaming around.
The only thing that the zombie movies have in their favor is the element of surprise, because it would take most people a long time to accept the fact that there really are zombies roaming around. However, people today are generally pretty paranoid even without the zombies, so I can't imagine anyone allowing a total stranger, who clearly looks ill, to slowly walk up to them close enough to get within biting distance.
However, the realities of the situation are not a part of the fun of zombie stories.