Well, if glass is subjected to a temperature drastically different than its current temperature (generally on the order of 100 degrees or more Fahrenheit) it will more or less shatter all of a sudden; the stuff is very hard (far harder than steel) and brittle as a result; thus damage to one part quickly spreads throughout, which is why in most cases, you can't just break a small hole in glass; the whole pane, even a large one, shatters spectacularly.
Claims of them rocketing a good distance are perhaps too fantastic to believe; that'd require several joules of pure kinetic energy to launch it that high; that' be converting a lot of heat to momentum. However, shattering the glass wouldn't be a problem, or burning it up.
It's common practice for big corporations like Apple (or Ford, as mentioned above) to try and deny any responsibility for the failures of their products, ESPECIALLY if people get hurt or property gets damaged as a result. Making good products is NOT their goal: making money is. And admitting they screwed up, while it might go toward the former, it hurts their odds at the latter.
So all told, I'd guess that yeah, there's heat issues with the iPhone 3GS, (which is no surprise; I remember less-serious heat issues with some of the first PowerMac G5s) and predictable enough, Apple is hoping a straight-faced lie will allow them to avoid any responsibility until this "blows over."