Investors (and financial Las Vegas gamblers) are betting that the results of the referendum will force Greece into yet another "compromise" to keep them in the Eurozone. The Greeks will pretend to cut spending and actually raise taxes, and the lenders (primarily French and German banks) will pretend to believe them.
The US markets are watching this like a drunk who woke up with an ugly girl and a bad hangover. They have to believe they will sober up and the woman will eventually leave, because there is no "Plan B."
Our own markets are hopelessly inflated, propped up by nothing but lies and thin air.
The NASDAQ 100 is selling at a PE of ±20X and I think that's just about right for a growth sector. That's not hot air...that's cash (earnings) on the barrel head.