Depends on what part of the city you wish to reference
With a population of 8 to 9 million, there is a complete range of economic strength, including several highly populated areas with relatively dismal economics (A lot of Harlem; South Bronx, portions of both Queens and Brooklyn)
As you've likely already deduced based on the tenor of the posts within this thread, by far the leading reason why the cities cited in the lead post are economically depressed is because for between 80 to 100 years, they were all founded heavily on a manufacturing economy.
NYC, on the other hand, while it has a wide range of manufacturing, also has a virtually endless list of other industries; is the financical center for the eastern half of the USA and attracts literally hundreds of millions of out of town visitors annually.
See:
http://en.wikipedia.org/wiki/New_York_City
Imagine Berlin x about 3 and you're getting a fair sketch.
Meanwhile, the cities listed in lead post all have populations under 1million, with most averaging about 300-400,000
When their core manufacturing industries crumbled during the mid 1980s-Today, there were far less legitimate economic opportunities within.
