A mindblowing statistic

In the context of all humanity, one city is not much to care about. However, this statistic made my jaw drop. From a lengthy piece on Hong Kong's "Umbrella Revolution":

Twenty percent of Hong Kong’s population is living under the official poverty line, but the city’s 50 richest people, according to the annual list compiled by Forbes, are worth a total of $236 billion (Hong Kong’s entire G.D.P. in 2013, by comparison, was $274 billion).

Historically, has it generally been the case that the richest inhabitants of a city are worth almost as much (86%, in Hong Kong's case) as that city produces annually? Is this normal, in other words, or is Hong Kong a sign of just how rich the rich are these days?