There is a large, technically illegal, economy to NYC which doesn't appear in W-2s, 1099s or self-reported census income, that most people outside of it generally aren't aware of. I'm not saying that the situation is good, but "60% of New Yorkers are not earning a living wage" is inaccurate. The existence of this grey economy makes it very difficult to measure income and expenses for a large proportion of New Yorkers.
[edit]: As an example, I have a friend who grew up in a working class family in south Brooklyn. His mother's job was "on the books" and his father's construction work was completely off-the-books, paid in cash. Everybody in the family was very aware of the amount of money you could deposit in a bank account, in a given time period, without attracting IRS attention.
Recently, they bought a building in Brooklyn for a low million dollar figure, after pooling together informal loans from family members and friends. But their household was probably below the "living" wage, from the point of view of this data set, for the past 25 years.