Both my son and my hubby still open doors. My son because I raised him to, hubby didn't do it before we got together but it's second nature to him now. The first time he did it for his mom she about fell over. To be fair, they both open doors for both men and women. But I was raised in the south by southern parents who were raised by southern parents, etc. so manners were taught at birth. My son actually got in trouble in the Navy for saying sir when he wasn't supposed to. Finally his superiors were just, you know what, we know you were raised in the south (as if his accent didn't give that away) so we are going to give you a pass. He told them thanks, since he knew somehow I would know if he didn't say it. My brother's girls were born and lived in New York State until they were around 5 or 6 so they just said yes and no to adults. It didn't take them long to learn that wouldn't work with me or my mama or even my son. Why my brother didn't teach them to say ma'am and sir when he was raised that way is weird since he still does it.
Are we as a society losing manners, are the idea of what manners are changing? Most likely a little of both, but to quote one of my favorite movies "South Pacific" "you have to be carefully taught".