I'm not an expert on New York's history, but in a general sense, I don't find the clustering of buildings all that surprising. After all, what's the alternative? Highrises built sporadically around the island in isolated areas? A blanket of highrises covering the entire island? Once an area becomes established as a center of business (for whatever reason), there's a real benefit of living and working in close proximity so consequently other developments take place in the area.<p>Apart from NYC, it seems to me that roughly every major city I have ever visited had the exact same clustering in certain areas.