NYC was minimally affected by the real estate crash because of the ubiquity of co-ops, whose boards were not going to approve an onslaught of people with wealth that was only on paper or that were speculating on them as investments rather than using the dwellings as their primary residences. Prices dropped some, a little more so in the outer boroughs, but where did you see "10 - 20%"?

The real problem with buying an apartment (as I see it) is that you don't really have most of the benefits of "ownership" aside from cost and location stability, and even that is somewhat in flux due to association/management fees, and if you have a co-op., mortgage rates. But, it's worthwhile for some, and IIRC, the return was better than the S&P 500 from 2000 through about 2013.