Value certainly is related to owned assets and profit, but in the case of things like the Dow Jones value is more related to perceived confidence in the economy. If people believe their stocks are going to lose value soon they're going to try to sell before the value is lost and the increased supply of stocks on the market causes the price to sink. That's just basic economics, but when that starts happening across the entire face of the stock market with every company that shows unrest in the economic state of the US.