I'm not so sure...I've had people throw me with my elbow not completely straight in hiji shime, but the lock went through to the shoulder anyway, and I had to take the ukemi. And it was someone smaller than I am who did it. When I attack yokomenuchi my arm is in kamae position...not completely straight...but when my teacher does hiji shime he doesn't have to twist or torque the arm; he breaks my balance, I float for a second, and the lock is on. I also know people who have defended themselves from attacks using this technique.
So I see it used in newaza, standup attacks, and dojo situations. Doesn't seem so magical to me...not to mention that if I apply it standing and the elbow doesn't lock out, I just remove my feet from the ground and WALA! we have a reclining pin! Ok, and maybe uke has a hyperextended elbow...but what the hey...you can't have everything...
Ron