That kind of testing would be utterly rediculous overkill because the device would never experience anything like that in the real world and that's why CR didn't do it.
So you're saying the only stress the iPhone will receive in the real world is pressure against the direct center? It is much more real world to test multiple scenarios, because the real world tends to be random.
If you want scientific tests to mean anything, you've got to be meticulous. That means testing under multiple conditions and trying to account for as many variables as possible.