Erik Brynjolfsson looks at the data and asks: why do millionaires love New Jersey? My answer: because it's really, really nice!
Especially if you are old. You don't have to live in New York or Philadelphia, and yet you have access to at least one of those cities, possibly both if you buy in Edison. You can have a splendid house in a nice, leafy neighborhood with reasonable public services, a socially excessive amount of parking, and good restaurants.
For smart young people, however, the nice parts of New Jersey are very much a net exporter. The young ones can't afford the nice homes, they want the sex and excitement of the big city, or they want a higher standard of living in some less crowded part of the country. That in turn makes the nice parts quite "mature", which in turn attracts more old people; have you ever visited Montclair or Upper Saddle River or the nice parts near Princeton? These towns are perfect for 59-year-old, slightly boring millionaires (NB: I am not saying that Krugman is boring).
I left New Jersey at age seventeen, never to return, not to live that is.