Yeah, that's another big factor. I think American who live on farms or out in the country side tend to take their shows off at the door. Many old farm houses are actually designed with an area called "mud room." It's usually on the side of the house and where work shoes and coats are kept. This way if you're muddy from work you're not tracking the mud into the house, but the front door for guests is clean and guest don't have to take off their shoes. Some of these country houses will have cement or gravel side walks that lead from the drive way to the front door. So if someone just came from their house to visit their shoes are clean and it's fine.
If you have a visitor that's helped do some work, or kids have been outside playing and got dirty, it's understood that they should use the side door and clean off in the mud room and take off their shoes.
We lived in an old farm house for a while, but didn't raise anything while there. Mom kept old towels in the mud room and that was where us kids usually came and went from the house.
Some places in America are wet and muddy, others are dry, some are filthy cities, others are nice beautiful country side. I think most places kind of develop their own sub culture and they think it's the same all over America until they do more traveling.
Most movies take place in Los Angles California (hot and dry on the West coast) or New York (cold winters/wet a lot on the northern Eastern part) Both of these are big cities. While both places have large populations, they can't accurately show what America is like for most of the population.