It seems in general, colder climates with potential snow and mud make taking shoes off a priority. Warmer countries do this far less often. Here in Australia, it'd be seen as pretentious to be the sort of person who had to keep their carpets neat and clean unless there were religious reasons for it. So most houses have shoes on as the norm, partially because of the casual way Australians tend to live.
I've lived in houses with both rules as the norm and frankly, I'd prefer a dirty carpet to having to put up with foot odour, particularly if people have just been out walking somewhere. Some people would rather have their place smell like unwashed feet than have to vacuum more often.