You're ignoring international capital flows. The US has the least worst economy among the industrialized nations. Europe is edging close to a war that will almost certainly be nuclear. Capital is fleeing to a safe haven, and right now we're the safest haven of all even with our current problems. International capital flows go mostly into the Dow, which is the index that is showing the greatest gains.
Besides, where else are people going to put their money? Real Estate isn’t a good investment at this point.