However, primary occupancy in the major properties under discussion here (the three along 57th plus the Time Warner center and a few others) is incredibly low, and basically speaks to high-end real estate bubble. These are high-visibility properties that people think of as good investments, whether because they can be re-sold later for similar valuations or because they're hedges against russians or chinese having to leave their own countries for a variety of reasons.
In that regard, it's totally worth noting that NYC does a much better job than most cities at permitting the construction of new luxury units that keep billionaires from pricing everyone else out of the market while extracting concessions like low- and moderate-income housing or the building of new parks. Imagine if each of the 104 billionaires who bought at 432 park ave had bought their own greenwich village townhouse instead. Supply would be as short as it is in san francisco.
That said, we can extract a lot more from builders and billionaires along the way, and we should. NYC still needs more housing -- the small proportion of rent regulated housing that accompanies these buildings remains insufficient to build the quantity of housing needed to avoid pricing actual new yorkers out, and to keep offering the services the city deserves.