Actually the DOR and the Ute offer decent 'give' balance with the mounting brackets (these will bend with the bumper in a strong enough impact). True the impact is stronger and earlier with aftermarket, but if you are talking the same impact amounts (speed, weight, etc) between aftermarket and crumple stock if you hit with aftermarket with enough force you'll see the bumper, mounting bracket bend, THEN the frame bend if balanced correctly. I would say that most of the time damage would probably be limited to bumper, bracket, grill, and maybe the front cooler if outfitted with a winch and a sufficiently strong enough hit occured. Probably driveable to nearest help.
The same force on stock would take out bumper, grill, push thru all the coolers,would take out front fenders, headlights/turnlights, fan, hood, batteries, crossmember, frame bending, and have internal engine compartment damage. Probably NOT driveable to nearest help. If it came down to it I'd rather have my frame straightened alot after an impact than to fix all of that and still have to have the frame fixed even if the frame damage is less by crumpling. Basically, the other stuff is giving it's life to lessen frame damage.
Also I would think that the majority of all 'accidents' concerning the front bumper with these trucks tend to be less than 5 mph pole tags or other taps on objects. And of course most 1-5mph pole tags are survivable over and over by the aftermarket whereas the stock will suffer considerably more damage and require expensive repair cost/time after each one.
So, that said, the answer to your original question is "the bumper/ mounting brackets have been bent on impact prior to damaging the frame. " This from Layne at DOR talking about accidents and someone doing a 90 degree truck retrieval from the ditch using the integrated winch. It's possible to bend the frame without bending the bracket or bumper but you would probably have to constantly hit stuff over and over again at low speed to achieve this effect but at that point it'd have balanced out since you didn't have to fix the crumple zone each time either. It's just a matter of answering one question, "Is it worth it for you?". Good luck!
Brian