Not to make a sweeping statement but I have found the Middle class do not seem too bothered about manners. I am not saying all but in my experience the working class seem more inclined to know when the "Thank you's" are needed.
The friends that come from the same background as me, albeit they now have the trappings of a richer life, seem to encourage their children to write thank you letters, email the same, and are more inclined to be polite.'
Hahaha! That's exactly the opposite of what I just said! Seriously, it's your experiences of course and it's good to hear different POV's hey? You could be right. Growing up in a W/class town, I have experienced every kind of person, mostly W/class, and they have all been often very different; there are classes within classes. And, W/class people in general do have a culture of welcome and generosity and a kind of 'mateship' that other classes seem not to have so much, but want to copy! Of course, there is a rough element in the W/class too; but there is good and bad in all groups of people.