Sadly, it is probably a metallurgy problem. Companies get stock from steel suppliers, who in turn make it into a machined part. In the nuclear and aerospace industries, such companies get paid to do their own metallurgical tests, and have x-ray vision or whatever to look into the steel to see if their is an air bubble or something. I've seen cracked crankshafts, where you can see clear as day once the thing has split open, that there was a void in there. Stuff happens. It doesn't mean the company that built it isn't a good company or it isn't a good product. It just means they were unlucky. You have to remember there are thousands of these things running around without issue, and that we as a society always like to sensationalize the bad things.