I've found that it's largely regional. In the Midwest, or colder climates shoes off is expected. There's just too much snow, dirt, and other stuff floating around for half the year. The other half it tends to be rainy, so now you're dealing with mud.

Contrast to the American southwest, where it's dry and hot all the time. You're not going to get mud in the house if there's no mud anywhere.

I live in Minnesota, and we keep a stack of slippers around for guests so they can take their shoes off, and still keep their feet warm.