Toby and Brently,
In my humble opinion, based on my limited experience, I would have to say that I agree with you both...to an extent.
In regards to the pycho-cemical stress. I know that in our school, from the begining, we go through a progression of "fear break-down" training. First by learning rolls and falls to get over fear of the ground, on up to fears of being grabbed, punched, choked, held down, pinned against a wall, struck with sticks, knives, swords...etc, by singular and muliple attackers. The situations can be quite stressful (especially when live weapons are involved, I personally have been cut-still didn't drop my sword though)
What we strive for is the elimination of the stress responce.
I don't believe that, for the most part, just anybody is cut out for this(no punn intended)or the "higher level" aikijujutsu. I've seen those that, regardless of the "qualified teacher, a willingness to learn, proper training and practice" will never really be able to use aikijujutsu to defend themselves in a real situation, or have the level of bodily control to do them. Some people just have fears that they can't get over.
In regards to using the simplest techniques on the street. Well, your going to use intsictivly those techniques you've practiced the most. Basics.
I know in our school we practice basic technique far more than the adavanced aiki techniques.
I spent six years as a bouncer,in situations that involved multiple attackers and weapons, and I never HAD to use anything but the most basic techniques. The situation just never required it. This was before I began training with Don, but my training none-the-less made everything seem as though it were in slow motion.
Besides, I think it really depends on what kind of aiki techniques your talking about. There are very simple distractions, on up to throwing without touching. In our school Aiki techniques are those that mess with the attackers senses.I think that the advanced techniques, in some cases, are really for the lessons they teach and the skills you aquire in learning them, than for practical application.
Incidently, those who have attended Don's seminars really haven't seen any of the basics we practice. He really only demonstrates the advanced stuff, and rarely are we allowed to play with it. There is a much harder-less aiki form of jujutsu, including striking and kansetsu waza that we don't get to show.
Also, in our school anyway, you have to go through training in "lower level" techniques, which often include aiki principles, before learning "higher level" techniques. More often than not the "higher level" stuff is just a different application of the basics.
In regards to the the original question.
The main difference, physically anyway, between jujutsu and aikijujutsu is that in aiki you try to take control of the opponents center right away. This allows you control of the whole body. I've often seen, and experienced, jujutsu techniques that only control the limb, and try to use pain to control the attacker.
Aiki does achieve this through skeletal locking, though they are much more subtle, less overt, connections that don't always feel like locks. Some cause the opponent
to "tense-up", causing the opponent to flex his muscles, thus holding or "locking" the bones in place, giving a connection to the center. Others achieve this through extension, "taking the slack out" of the body between the point of contact and the opponent's center. Still others simply lock the bones so subtley that you hardly notice it happening until your on the ground.
Well that was far more than I was originally going to say so I'll stop now, besides it's just my humble opinion.