Luxury apartments are lucrative, sure, but if you can fit more rooms into a given space you can often make even more money. For example if you could have 1 apartment and charge $3000, or 2 apartments and charge $1700, the 2 apartments are a better deal.
Citing Hong Kong struck me as odd. It's probably better being homeless in certain states. I think most people have seen the following, or similar, set of pictures about Hong Kong micro-apartments:
http://inhabitat.com/exhibit-on-the-micro-apartments-of-hong...
http://en.wikipedia.org/wiki/Cage_home
Real urban planning has low income housing distributed throughout the city. If not, the wage slaves have to be shipped in. Some form of rent control/social housing incentives have to be in place. Otherwise you get situations in the states where welfare mothers have to bus 3 hours each way to get to their minimum wage job.
Also without rent control, you will suddenly find cities suddenly very empty of people able to do things like get you your coffee. And shipping them in every day from 100 miles away is a dystopian nightmare.