GM, like the rest of the Big Three, are bellying up because of poor business decisions, labor costs, and the payment of retired workers. It seems like the auto industry pays more to its former workers than any other industry; my grandparents on my mom's side worked for Ford and Christler, and they're getting paid huge sums of money on a monthly basis. That takes a toll on a company after awhile, and there's nothing greedy about admitting that.
Ford is moving into the same position now, and they're making poor decisions. They kept building trucks and SUVs (which are actually cheaper to produce than their other vehicles), and then BAM $3.25/gallon gas prices pop up. People aren't going to buy trucks or any cars with terrible mileage with gas prices so high, and Ford simply did not anticipate that; poor judgement on their part. Even now with gas so low, their vechicles are still preforming at a mediocre pace.
I live in Michigan, so I see this happening before my eyes. Michigan has always been a manufacturing state, but now the manufacturing jobs are dying or being moved out the country. Is it Ford's fault that people are more interested in buying Japanese cars, and China's cars are right on the horizon? One could argue that the lack of innovation in their car design is a factor, as well as the mindset that foreign cars are of better quality than American ones (which isn't misguided). Labor costs are another issue. When you're paying someone $10 to put a screw in a hole for a few hours...