By far the overriding thing keeping Manhattan real estate prices high is housing regulation.I'd argue it's actualy the proximity to wealth. Hamptons is not regulated, and look at their prices. Finance, Law, medicine, and Media are all either pyramid pay or actual legal monopoly businesses. The rest is made on inside information, that stems from access that wealth brings to political, academic, and philanthropic circles. Not that there is anything wrong with that, its just how the 'world works' in many ways.
In any event, real estate is the ante to play the game. The proximity to power breeds value for two reasons: lust (in those who lack power) and practicalities (for those who have power, and want to keep it). Its worth noting that owning real-estate is about excluding other people from using it. High real estate prices force out competitors that migh otherwise use the assets to create a competing culture.