So you want a picture of a shattered glass with particles embedded inside the cracks? That could be faked too.
Or do you want a Mythbuster doing a special on them? N=1 as they usually do for experimental replicates is not very rigorous scientific method.
I guess somebody better buy a batch of 1000 iPhones and said cases and do properly designed experiment. But wait, results can be biased in experiments too!
If you are going to skeptic about things, nothing's going to be enough to convince you. Besides, as the article states, this started from an inside source saying Apple is looking into the issue. Likely they were getting more shattered iPhone 4's than they expected and so they are looking into the cause of it. And they probably found that this was the most likely or plausible cause of the case shattering.
No need to get your knickers in a bunch, the mob hasn't got out the pitchforks and torches to burn down Apple HQ just yet, and Apple is just trying to prevent some bad publicity and angry customers whose shiny gadgets are not as shiny any more. There is no conspiracy going on here, and they are not out to smear your favorite gadget supplier(s).