People lie. Especially when the truth will cost them a couple of hundred. I've seen cracked LCD screens that 'just happened' and had nothing to do with leaving a set of keys on the keyboard while closing the lid. I've seen mould growing off a sticky brown-stained motherboard that smelled of coffee despite the user saying that they never spilled coffee on it. I've seen squashed iPods brought in for 'warranty' work because the end user didn't think that leaving the iPod in their jacket and then using the jacket for a goal post in a soccer match was any reason for concern.
People lie. And people don't like their insurance to way out when they can moan constantly and get a new machine for free.
I see no evidence that these 'explosions' occurred and I see plenty of evidence that people lie when they break their computers. Apple is politely saying "You broke it, you fix it" which is fair enough for any manufacturer.