Not only does over or under inflation affect tire wear and fuel mileage, but it can seriously affect the safe operation of the vehicle too. Tires with the wrong amount of air in them cause the tire to fail, perhaps even blow out while on the highway. It can also change the way the vehicle will react in a sudden emergency maneuver and that can cause an accident that might not otherwise occur.
When the labels have the wrong tire pressure numbers on them, during the life of the vehicle the odds are that some future owner is going to make a costly mistake. It can lead to an accident. That's why recalls are sometimes issued to fix mislabeling problems. Here's a recall for just one such problem.
Do you own a lemon Airstream?
Do you want a new Airstream?
Do you want your money back?