Poundstone is awesome and an incredible athlete, but at the same time, he's certainly not natural and has a LOT of experience under his belt, giving him a bit more reason/ability to push his boundaries beyond what most natural lifters can do. Going to failure from time to time is a good thing, but it's not essential to making progress, and too much of such a thing can hinder recovery and ultimately lead to less overall progress. For example, if you set the "to failure" bar too high from the start, you may find that you won't be able to complete training programs that you wish to follow, as going to failure on everything isn't always feasible. For example, if I wanted to do 5x5 in the squat and I went to failure on that first set of 5 reps, the smart money is that on each set, I'm going to do less and less and by the end, I'll be lucky to squeeze out 2 reps. The body of a natural lifter just doesn't usually have the capacity to keep pushing to where you can't go any further each and every set, so usually, I'd suggest saving the set to failure for whatever your last set is that you're wrapping up with. So, using the squat example again, if I got through the first 4x5 easily enough, I might see how many more beyond the 5 I could knock out on the final set only - even if I could get one extra rep, it would show that I'd gone beyond what I set out to do, and that would let me set the bar higher next time for the same lift, either adding weight or adding reps.
What should definitely be admired about Derek, though, is the intensity he brings - nobody is going to be a champion like him if they say "I did 10 reps, could have hit a bunch more, but that's enough for now", because when you compete in strongman, that just won't cut it, and you'll find that you'll be at the bottom of the game compared to others who push as hard as they can. Remember, when Poundstone is competing, it's all about how many reps you can in a set time, how fast you can flip a tire for distance, how quickly you can pull a truck for distance, etc., definitely not what bodybuilders or powerlifters ever need to be prepared for, so it's a whole different game!
"A 'hardgainer' is merely someone who hasn't bothered to try enough different training methods to learn what is actually right for their own damned body." - anonymous