The point is that Detroit going broke didn't bring all the capital markets in the US to their knees. It's definitely not good that Detroit went broke. But it didn't break the US economy.
Note that "wasteland" is exaggerated. Certainly there are a lot of abandoned buildings and neighborhoods, but many places are still thriving. It's not what it once was, but there's still a lot going on.
Seems that there are a lot of stakeholders who are care a lot more about not having Greece default than was the case for Detroit, while at the same time nobody has enough power to really make anybody do anything. So Greece is coming down to a very long and drawn-out series of negotiations where nobody can put their foot down and say, look, here are the lines you can't cross, and here's where you're allowed some flexibility. Figure it out.
With Detroit, it all happened in an environment with a strong legal system that could keep the various parties under control. The fact that federal (and even state) benefits aren't affected by Detroit's finances no doubt helps a lot too. No matter what happened with Detroit, 70-year-old retired autoworkers living there would continue to receive Social Security. That simplifies things a lot since there's a backstop for how bad things can get in the worst case.
If Greece were given enough to tide them over for 10 years how do you think the government would spend it?
Debt management is about a partnership, where financial responsibility is learned but both sides. The creditors are learning to be more cautious and Greece is/has learnt to control its spending.