Conor Friedersdorf makes the case that New York is too dominant on the American landscape. The principal reasons seem to be that it lures talented people away from other cities, and that it appears too often in television shows and movies. I'm unconvinced (both that it really is that dominant, and that the reasons he mentions really matter all that much), but it's interesting to ponder nonetheless.
If you compare it to many other nations' great cities, New York really isn't that overwhelming in this sense. It shares cultural preeminence with LA, and is clearly behind Washington as a political center. I imagine London and Paris monopolize their country's existence more so than New York does. Mexico is the country about which I can speak with the most authority, and I'd say that New York's role in the US is significantly less than Mexico City's in Mexico. Here, the percentage of movies taking place in Mexico City is probably around 80 or 90 percent. (Off the top of my head, I can think of only one recent flick in which Mexico City doesn't appear: Seven Days. I could name twenty without any trouble set in Mexico City, often with the Mexico City-ness a major element of the story.) With novelas the number isn't so dramatic, but most are also in Mexico City, especially those set in the modern era. Mexico City is also home to about 20 percent of the nation's population, compared to roughly 5 percent in New York. It's the unquestioned financial and political capital. It's also physically smack dab in the center of the nation. Elsewhere in Latin America, the story is similar: Santiago is home to a third of Chile's population, as is Buenos Aires in Argentina. Both are the financial, political, and, I presume, cultural capitals in their respective nations. I invite better traveled people to comment (especially New Yorkers who know Mexico City, and vice versa), but it seems as though the US is more on the multipolar side of the spectrum.