We're not teaching manners as a society. Not often, anyhow.
I've got kids and I always made sure that I modeled manners in front of my children. "Excuse me, Pardon me, Thank you" are all utilized in my family...and proper behavior is insisted upon.
I find that many parents I see of 'yuppie' status seem to have an 'entitled' attitude...their kids don't say anything except "I want..." or "get me...." And I see where they get the attitude from when I meet the parents. It's "me first, I'm important, pay attention to me" like nobody else matters. A real nice example of this is the old 'Kate + 8' trainwreck...watch Kate and Jon Gosselin and their kids and notice how often both parents fail to model good behavior or social graces. I don't think Ms. Kate realizes that when her children hit the teen years, she's going to pay for encouraging that 'entitled' attitude...but then, you can't tell her anything, from what I've read.
I was always taught that in order to get respect, you have to be respectful of others...and a huge part of that is manners. Both of my children exhibit behavior in public that I am extremely proud of...they are respectful and thoughtful people because I emphasized that as being important.
And just an observation...food for thought here....on occasion, I've had the pleasure to interact with a fair amount of Canadians. Their outlook is 'community first', not 'me first' as it is here in America. Thinking about others is encouraged, not ignored as being provincial and backward. Maybe if we got back to our small town roots, where being a part of a community takes the focus off ourselves and on others, we can get back to manners in this country.
I'm glad you do your part and you're not alone...but I know what you mean, it sure feels like it sometimes!