Most people here are opposed to socialism, communism, and class warfare. They don't understand that adopting the terminology of class is opening the door to that. Read Sociology in Wikipedia if you think I am exaggerating. I believe that it is also explicitly unconstitutional, (I think the constitution bans all titles) though I have not had a chance to look that up.
Before 1964 certainly black Americans constituted a separate class. That is as far as I will go. Calling arbitary income groups classes os not only wrong, it is subversive.
Most people have enough intuition to know what is meant by "class"--a couple of days ago, when a malicious Chris Matthews managed to stage a rude treatment of Ann Coulter, the crowd fussed and Matthews said, "Hey, is this Deliverance?"
Now, the non-sociology teachers among us know that he was calling the audience Poor White Trash, or rednecks, or uncultered bumpkins, but we all got the point pretty quick. It was a class insult from someone who obviously and mistakenly thinks he is socially/culturally/morally ascendent. The whole Deliverance story was a kind of class warfare, a confrontation between two ways of life in America.
It's true that Americans don't wear caste marks on their foreheads, which is something you seem to be insisting to allow for the existence of classes--but there are all kinds of degrees of class and class consciousness. Dare I say "nuance"--a word I've also come to hate by the misuse by liberals. By denying this, you certainly take a lot that is interesting away from the study of society. Veblen, Epstein (not a phD, but a darn good sociologist), even that simpy Brooks guy on the NYTs.
There'd be no Wharton, no Tom Wolfe, no Magaret Mitchell--without the consciousness of class.