This is NOT TRUE for New York City. Unlike the rest of the country, New York real estate appreciates in value - guaranteed. What you don't know:
1. Co-op buildings in NYC have down payment requirements averaging 20%+. Co-op buildings in the nearby suburbs average 10%+ for down payment requirements. Because of these high down payment requirements, co-op Boards do not allow FHA, VA and other loans that have low down payment requirements.
2. Co-op Boards review a buyer's financials before buyers can close and can legally reject buyers based on their financials. This means if the buyer was approved by a lender, they can still be rejected by a co-op Board.
3. Because only qualified financially secure buyers move into a co-op building, the value of the entire building increases in value and appreciates. Condos in NYC do the same. The Board of Directors has first right of refusal and if they feel a buyer will default on the HOA fees, the condo board will refuse the buyer. Just like co-ops, condo buildings do not have to allow FHA or other financing that has low down payment requirements. Co-op and condo buildings only want buyers who can put some of their own money into the home purchase.
4. During the housing crisis / recession when the rest of the country was suffering from foreclosures and short sales, New York City did not suffer much thanks to the verfication of buyers financials and down payment requirements for condos and co-op buildings.
Therefore, buying in NYC is expensive but you don't have to worry about your investment. It will appreciate. There are exceptions to this: Examples: bad neighborhoods that are mostly welfare residents and/or have a high crime rate; the immediate area surrounding JFK & La Guardia; etc.