Kaineng is pretty much the Guild Wars equivalent of an urbanized city in China, or Japan. It's a major port city, which implies a huge amount of import and export, not to mention that it's the home of the Xunlai, who are apparently the "world bankers".
I imagine Kaineng used to be a major port city, which rapidly exploded due to foreign interest in goods and material. The Slums and poverty is the result of massive immigration to the area, from peasants seeking to make their fortunes after hearing about the wealth of the city.
I highly doubt that it's self-sustaining, instead relying on goods from the other parts of the continent, and from other continents and nations, to provide the necessities of life.
Notice how Vabbi, the other "wealthy" nation, seems to have a more classical version of wealth and luxury, while Kaineng is very much a commercially wealthy area.
You know, though, this could have some very interesting implications for GW2, when the entire continent is cut off from the rest of the world.