The USA is nothing like Greece. Greece's economy never was very strong and has been defaulting on debts for 200 years. The US has never defaulted on a debt. They have been living very deep in debt for many years (more debt than GDP, something the US is not close to). They also have had runaway inflation while we have not. Invoking Greece is just hyperbola.
We won't technically default on the debt. We can just print enough money to pay it but of course, the dollars won't be worth anything. OE2 will be followed by QE3 when the economy doesn't respond. The FED is like a gambler that is down and can't pay. He just doubles the bet til he either breaks even or the amount is so enormous that it is obvious he won't pay.
