I don't think it's one or the other ("taking ukemi" or "being thrown"). There is a continuum that ranges all the way from letting a 5-year-old execute kokyunage on you, to finding yourself on the mat and not even knowing how you got there. The latter has never happened to me, but I've felt quite a bit of the scale over the years.
I could see how the possibilities of experiencing the higher end of the scale would diminish (potentially to zero) as one's own abilities (or whatever
) increase relative to those of the people with whom one is training. Under this conception, O-Sensei might experience everyone the same way I experience training with my kids' class.
I think this is the point Chris and Dan are trying to make. It makes sense to me.
Yes, I agree that there is a scale, but I don't think that is really the relevant point. That "unthrowable" stability is the expression of a certain kind of practice all by itself - that would be a little bit closer...