Korea...But Gorilla Glass has a fracture toughness of 0.7 MPa*m^0.5 while aluminum has a fracture toughness of around 20 MPa*m^0.5. So given the presence of an initial crack, the gorilla glass is much more likely to fail in brittle fracture while the aluminum would be more likely to fail through fatigue.
Gorilla Glass has a high resistance to scratch damage compared to a soda lime glass and is thus less likely to initiate a crack by the user. However, if an initial flaw occurs at manufacture it will likely fail in a brittle manner.
One thing I’d be interested in knowing is if this glass is being made by Corning in China. If it is, I wouldn’t be surprised to find out that the problem with the glass is from manufacturing defects and not from user scratches. The glass might be failing when an initial flaw is present and someone puts the case on causing a load that raises the stress intensity factor at the crack above the fracture toughness of the glass. If so, my advice to Apple would be to have the glass made in Korea, Japan or the US and ship it to China for assembly.
Korea... From what I can find out Corning makes Gorilla Glass under strict quality control. There seem to be very few complaints about such issues among the users and the articles evidence, I.e. , the non availability of slide in cases in the Apple stores is bogus, makes the story FUD.