What day of the week is it?

It struck me today while at work the funny way that we tend to answer questions in our society/culture. When somebody asks you "How are you doing?" or "How's it going?", they generally don't expect you to truthfully tell them exactly how you are and if you do answer truthfully, they usually will be stunned and left speechless because they don't know what to do. "How are you doing?" is definitely more of a greeting, like "Hi", "Hello", not a genuine question and concern. It's funny when you really think about how we respond to people. Today at work, I heard at least 6 or 7 times the reponse to the above question "How are you doing today?"as: "It's Friday". I'm sorry, I don't remember asking you what day of the week it was, I remember asking you how you were doing. Where does the idea come from that an answer of "It's Friday" suffices as an adequate answer to the question "How are you doing?"