They were all shot in Spain by Italians, so both aspects play a part. David is right about the style; in some ways Sergio Leone epitomised Italian Realism, so they do feel different to Hollywood bred movies, but the locations aren't quite American, which adds to the extraordinary feel. In some ways, Realism is about not trying to hide that it's a movie, so they have that operatic and, as you say, mythical quality.