Word Maintenence

Did you ever notice how when people answer the door, they say "who is it"? Why, exactly, is it necessary to speak in the third person? No one ever asks "who are you?", they just like to pretend they're an actual speaker in the wall, and not someone behind it. I'm just as surprised people don't get mad. Have you ever heard a mother freak out because you ask what "is its name?" Nah, I think the first person is a much easier tense to work with.