The general consensus that Consumer Reports seems to be getting at here is that the results that they observed shows that while the iPhones do bend, the amount of force required to do so results in phones from other manufacturers simply breaking under the stresses involved. It also appears that Apple may have done some investigation into the engineering behind what is "good enough" behind the stresses that a phone needs to endure, much as traditional building codes have adopted. Looking back into the past, there have been great feats of engineering that have stood the tests of time and survived admirably, and a large part of that has been due to being "over engineered" than what was technically required, or from a simple lack of knowledge at the time of what really *needed* to be done to withstand the rigors of severe, gail force winds, earthquakes, or the like. Apple has fallen into the fallacy of "good enough" in an effort to reduce materials used, lower production costs, ease manufacturing, and all the while use those traits to leverage themselves as a positive for why the casing is thinner than ever before, lighter than ever before, and yet the product is now bigger than ever before. Less material, less weight, less volume, greater screen size... Uh. Something had to give *somewhere*, hence a product that is now less sturdy than it was a year ago. As such, they are likely going to have an increased number of warranty claims this year compared to previous years due to the folding potential at the structural weak point between the opposite inserts for the volume and power buttons.
Frankly, this is more a sign that they may have reached the point that using a highly malleable metal like Aluminum simply isn't a great choice and will ultimately lead to further structural issues like this in the future in the push for ever thinner, lighter devices that was exacerbated a little earlier than I expected due to the moving of the Power button. Long term though, there are ultimately ways around this through shifting to alloys, polycarbonates or carbon fiber and employing more complex geometry into the design, such as a honeycomb configuration as to allow for force to be dissipated through the surface rather than through a sudden catastrophic failure as they are seeing with the iPhone 6 Plus design due to the structural weak points of the recessed volume and power buttons on opposite sides of the casing that will itself only get worse over time. Should the buttons themselves been raised outwards so that they were not flush with the case or staggered so they were not adjacent with each other, while not being as aesthetically pleasing it would have resulted in a stronger, more durable product and I think that's ultimately the point for something that is intended to be with someone 24/7 for the next 2 years of their life.
End result is that life sure is easier for an armchair engineer to sit back and look in on why something failed than it is to see the forest when you're trying to make every branch on each tree "elegant".