I have heard a first hand account of Okamoto saying (in the middle of a seminar demonstration), "I'm not hurting them, I have no idea why they're doing this..."
There is a long tradition of trying to make your sensei look awesome, it's not just a DR thing.
hmm... assuming what you say is true, then it would make sense, because some of the similar techniques i've seen done in aikido do not seem to elicit similar reactions of pain. uke merely has their balance taken, thrown et cetera without the intense grimace on their faces.
it'd be good to have DR practitioners who have tried it first hand to share their own experiences as well aside from our hypothesising.