I think it's less of an issue of can they afford to buy in NYC, but can they afford to live in NYC, period.
Before most people buy, they have to rent, unless they are lucky enough to be able to live rent free with their parents. A rising tide raises all boats, except for the school teacher and cop earning $45k a year (and that's a typical starting salary for those solidly middle class professions), who have to shell out $1800 a month to rent a one-bedroom in Kew Gardens, that doesn't leave a lot left over to put in to savings to buy a down payment. And if one doesn't partner up, that person is almost guaranteed to be living with roommates well in to his or her 30s. Wages have been stagnant for decades, so the middle class actually isn't doing better than their parents and grandparents did a generation ago. The middle class is worse off.
When it becomes impossible for the people who educate our children and serve us in law enforcement to afford living in the city, let alone the people prepping your food at the restaurants we frequent, it's apparent there's a problem. I don't have the answers, but affordable housing is a must. A city simply can't function if only the upper middle class and rich can afford to live in it. Someone has to clean the streets.