I'd say that the distribution is likely that most of the people with a dead unit posted reviews, while most of the people who received a working unit have not (and are likely still playing it).

People are far more likely to complain than to praise, and a dead unit arriving for a fairly expensive hot commodity is definitely cause for complaint, especially for something people are so passionate about as a PS4.

I'd be eager to see how many of those low ratings were due to people who took the day off to play it and couldn't.