Cities are really efficient. You can squeeze more people and more activity per square foot than any other implementation known to man. But in doing so, you cause a whole lot of grief - traffic congestion, easy disease propagation, a general aura of increased blood pressure, etc
The amazing thing is, despite all the chaos and misery, the level of efficiency is still many times higher than if you did not have cities.
But that isn't exactly true - some cities like Copenhagen get a lot more efficiency than insanity, while in other cities like Bangkok, you'll be hard pressed to see any efficiency at all.
Sounds like a good heuristic though: anything worth implementing delivers a multiple of present results regardless of the quality of the implementation. ie: the most insane city is still going to get more done than the most efficient village.
But because the initial implementation can afford to be messy, it will be messy, and we all have to put up with a crappy implementation until sufficient time and will has passed to refine our solution.
However, with major implementations like a city, such refinement can take generations to occur. That's why I dont' live in the city =).