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Sadly, I think the manufacturers themselves- at least their public facing departments- don't understand the causes of these failures either, and thus their blame of the operator is not generally dishonest (though still wrong!).
There used to be a rich collection of similar failures, with insightful commentary, here:
http://pardo.net/bike/pic/fail-012/000.html
It seems to have lost a few pages though. Still, an interesting read.
Edit- ah, here you go:
Really useful and interesting, thanks. Sounds like a genuine and serious problem with the design and/or manufacture of these cranks.