Re: Locking/pinning as pain submission...
I think Larry has made a very good point regarding the nature of "our Aikido" and "Aikido." But I still think we can talk about the mechanics of something without having to address the definition of "Aikido" and thus the legitimacy of any one type of "Aikido."
Though I have seen Kisshomaru and K. Tohei do techniques like Rokkyo, I don't think we even have to go into this type of "non-pillar" waza in order to realize that Aikido waza do not go with the "natural bend" of the joint. We can simply take kote-gaeshi, nikyo, sankyo, yonkyo, gokyo, etc. - which I'm sure we all practice as well. Because there is no true ball and socket joint involved biomechanically, movement engaged at the joint will at some point travel against the structure of the joint and/or go beyond the joint's range of movement (hyper-extension). It is precisely because this happens that a nage can "connect" with uke's center via a limb (as was mentioned earlier in this thread). If the structural architecture of the joint is not in some way "locked" (i.e. falling outside of the natural bend of the point of articulation) energy would stay in the joint - not traveling anywhere. It's basic science - regardless of what Kisshomaru might say, he's wrong.
In light of the science, I think we should understand Kisshomaru's point as being akin to every such point made by a Japanese founder or doshu when asked to explain his art to the general public. Going back hundreds of years, one can read these same type of statements - where a martial artist over-generalizes (inaccurately) his art in order to contrast it against other arts (which are also over generalized) in order to legitimate his own art through difference (only the difference doesn't really exist).