Kenji Ushiro predominantly use Ashi Awase to unbalance his opponents (before contact) and then he proceeds to strike them. To most people who see this, they think the opponents are afraid of being striked by a ranking sensei and so they flinch. Most would attest to this if you ask them. Aiki is just obeying natural law. In this form, most would flinch as an automatic reaction, rather than a perceived reaction to an incoming strike. Its not magic, but its not preconditioned.
Actually, Ushiro Sensei uses his ki before any movement actually occurs. As a direct student of Ushiro Sensei, I can personally attest to this experience. It is simply impossible to convey what happens on a video. What you assume to be ashi awase, is profoundly below the level with which he is functioning at. That was why I advocated that a person reserve final judgment until a person has some first hand experience with a teacher. The "flinch" experience is best described by one of Ledyard Sensei's "Aiki Koans"-> What is the timing of already? The person experiences "already" after it is way too late. Personally observing this type of interaction is interesting because it looks as if Ushiro Sensei's movements are simply too slow for a person to not be able to track his movement. Unlike most Aikido practice, the people attacking him are well-trained attackers who would simply overwhelm most Aikidoka with their attacks. Practicing with these people is always a humbling experience that forces you to have to always advance the level of your own personal practice in order to get better. Needless to say, it is having a very positive impact upon my Aikido!