I've never been to Hong Kong but I've been to London and New York and I didn't see too many single family units near the city, which is precisely my point.
I find it interesting that the [predominant] type of housing is very different between cities. Some of that is regional (east coast, west coast, southern, etc.), but much of it is fairly local to a city. There is certainly an effect on population density, which might drive the growth of the city; but there is also a change over time in housing types which might be a response to growth.