I personally feel that it is very essential to cultivate the habit of saying thank you and sorry when it is needed either in public or with your close ones.It is a basic requirement , which helps us realise and appreciate help given by others and also accept our mistakes .
Pay no mind to those who talk behind your back, it simply means that you are two steps ahead !!!
but your close and near ones dont need that.its a dislouge from k2h2 no sorry and no thank you in friendship..even sometimes this thank you is not enough better do something in return instead of saying thank you.