The reason we Americans "in particular don't understand" this is because this is way less a *thing* in America, especially outside the Northeast. Sure, there's a distinction between "old money" and "new money," but we do not have a large distinction based on class that's not related to wealth like the UK (in particular) does. Money equals status in a much more real way here.  


Of course, people exist who come from "money" and what would be called called "upper class" families but are economically mid-range themselves. And there are people who start out lower-class but become fabulously wealthy and are viewed as being not as... refined, I suppose, as those born into money. But these class distinctions are not emphasized and commented upon and just something that is always in the mind of society as a whole *nearly*  as much as in the UK or other parts of the West.  


Instead of being hung up on class to such an extent.... here our big issue/social preoccupation is race. We can argue about which is worse.