Never been to NYC, have you.
Unpaid internships are nothing new at all. The idea is that they get the free labor in exchange possible college credit and real-world work experience that can be put on a resume when you graduate college. Some places have been known to hire back the same people two summers in a row and that makes it more likely that they'll offer the person a position at some point after graduation (if one is available).
In college, I was a paid messenger at a law firm on Wall Street. There were plenty of "summer associates". Granted, they were in law school, not college, but it was the same principle.