Upscale Apartment Trend

I feel as though large and lavish apartments have been a big trend in large cities at the moment. One building I was reading about on bloomberg was about Sulzberger's Fifth Ave. apartment in New York City. The "apartment" itself has 11 rooms, that's right, eleven. At what size does a dwelling stop being an apartment and becomes a mansion? It comes with three maids' rooms, and has a private library, all for the extremely reasonable price of $12.5. Did I mention that it also has a wood-burning fireplace? Just in case that would do the trick for you.