I agree that it crosses all ages. The other day we were going into the grocery store and this older man in a scooter was struggling to get in the door. My husband stopped and helped him through and he zoomed right on past, no "thank you" and missed hitting my two year old by a couple of inches in his haste. I was VERY put out about that.
Whereas, my two year old...if anyone sneezes ALWAYS says "Bless you" and when the reciever says "thank you" she responds with "your welcome." I would like to hope that we will raise thankful and polite children.
I agree that common decency isn't common any longer.