I don't see what the big deal is.
There zero cases of Volts having battery thermal issues after getting in an accident in the real world. There have been a couple of cases of garage fires, however the causes are not yet known and it is quite possible that the fault lies in poorly done 240V wiring, and not with the Volt.
There are four cases of Volt batteries having thermal reactions after being first disconnected from their liquid coolant supply, then damaged, and then overturned by NHTSA. This is like sideswiping a pole at high speed, at exactly the point where the battery extends out towards the sides of the car, then rolling over, and then letting the battery sit damaged for several days without being discharged.
Here's an experiment: smash a gasoline car in such a way as to rupture the gas tank. Then turn the car over and let the fuel run where it will.
Also, consider the number of gasoline vehicle fires that occur every year. In 1999, there were 288,000 highway vehicle fires, due to all causes (accident and otherwise), according to the NFPA. According to a 1990 study by NHTSA, motor vehicle fires due to accidents occurred at a rate of 2.86/1000 vehicles.
So if Volts had the same rate of accident caused fires as gasoline vehicles, we would expect to see about 14 Volt fires this year. But we haven't, even though Volts do carry gasoline on-board.