I grew up in Manhattan, and yet I'm baffled by how large my home county—20th in the U.S. in terms of population with slightly fewer residents than Broward County, FL—looms in casual discourse about urban policy. Ben Adler has a piece about Stanley Kurtz's paranoid screed about Barack Obama's alleged plot to destroy the suburbs in which he quotes Kurtz warning against Obama's plans for "regulations designed to force Americans out of their cars and into high-density urban centers, squeezing the population into a collection of new Manhattans."
It's a great example of a weird polarized discourse in which somehow either everything has to look like the furthest-flung exurbs of Kansas City or else Manhattan. But even in New York City the vast majority of people don't live in Manhattan. Both Brooklyn and Queens have more people. In policy terms I don't know where that fact gets you exactly, but I do think it's important to set a baseline. Manhattan is a strange edge case even within the confines of America's biggest and densest city. There's tons of middle ground between the current NIMBY disaster of Silicon Valley and Manhattan's 70,000 people per square mile.