for 1: America isn't the world. Ask the UK if they're still having Class issues. Or India. Or Japan.
for 2: Actually, the US has had an upper-class of sorts, although it's not as prominent as it is in Europe. The WASPs were about as close as we got to aristocracy, and those have more or less died out by now. But, if you consider the Rockefeller's or the Kennedy's to be "upper middle class", I'm afraid you're sorely mistaken.