I would have thought its very hard to prove either way, although it has been noted in the past of drive which spin rapidly enough to cause problems with disks. Also there have been reports of whole batches of disks shattering in drive. I fail to see how the "experts" at Sony could pin point it to the disk without experts on stress fractures in plastics.
One of my friends successfully an argument with Orange when his phone broke. They claimed it was accidental damage, he pointed out the it was a problem with stresses in the plastic (he won he had done a thesis on it)