Class structure in an advanced 21st century economy is a complicated phenomenon, and reducing everything to an income bracket is inevitably going to be a bit reductive. But when pondering a question like "What Is Middle Class In Manhattan?" considering the high cost of living and blah blah blah it is useful to go back to the basic Census facts. The median household income in Manhattan is about $67,000 whereas the median in the nation as a whole is about $53,000.
That's a gap—$14,000 is nothing to sneer at. On the other hand, this isn't some land of unimaginable wealth. In Maryland, the median household income is about $72,000 a year. Even richer than Manhattan! But you never read stories pondering what the real meaning of middle class is in Maryland.