Doko, apart from sounding like a [censored] with the way he posts, should have known that when you test a piece of software you must do it like an end user. I don't believe that they didn't do a full 300 hour playthrough on the PS3 before release but if they didn't, it is very unproffessional of them and they deserve the backlash.
The gaming industry sadly has no limits on work hours. Just google it.
Their machine may have been suped up in some way we don't forsee. Some change may have occured at the last moment or perhaps there was a ps3 firmware update that conflicted at some point.
There's a few things that could happen. But as a professional tester myself, I bet someone is very scared about their job right now and I wish them the best. It's rough to miss a big bug during testing. I love finding a big one and crushing the souls of our developers. I fondly recall dancing gleefully around one engineer when his three week long project turned out to cause fatal errors that could potentially ruin a server. It wasn't a nice dance, no, it was a mean spirited sort of taunt that could legitimately have resulted in fisticuffs. Fortunately, I was the bigger man. Physically.
But there are a lot of other variables that could have prevented testers from catching it. It may have come down to the testing project design itself. After a few more certifications I think I'll apply to Bethesda, I love their game and I love catching/solving bugs, so it's a good fit (though testing can ruin your love of a product).