Since I currently live midway between NYC and Philly, I can honestly tell you that two things happenned in the latter that did not happen in the former a. an exodus of the wealthy (dare I say, more important that the "middle class") and b. exodus of employers. Philly was once a manufacturing and financial center, but the former could not be sustained in light of cheaper and more efficient labor elsewhere, while the latter was eliminated through consolidation of said industry.
To think, back in the 1970s, we kept hearing about the dangers of the exodus of the "middle class" (Read: Archie Bunker) from the cities. NYC survived, however, while Philly (largely dominated by blue collar machine politicians) did not.
Nevertheless, there remain some nice neighborhoods in Philly (Society Hill, Chestnut Hill) which are bargains compared to NYC. However, would you really want to commute via Amtrak everyday? ;-)
NYC is about nothing but commerce. There’s no underlying philosophy or ideology, except business. So, it adapts quickly. What most people see as a “liberal agenda” is nothing more than either window dressing or grease to keep the machine humming along.