I think George Ledyard gave the best answers there. For the Ki Aikido person who said the Taigi didn't have atemi...if it looks like a duck, swims like a duck, quacks like a duck, tastes like a duck - well, quack. Some words I have had to just stop translating as the closest word in English is too loaded with its own meaning.

Roughly paraphrased from the Bubishi (the "bible of karate") and not an exhaustive list, striking vital points can be used to cause: distraction, illicited reflexes, movement, pain, impaired motor function, impaired sensory function, impaired balance, impaired respiratory function, impaired circulatory function, organ trauma, unconsciousness, and death. Aside from death, most else can vary in severity and duration.

Kenji Tomiki was one of the earlier students of O Sensei, and he developed a set of atemi waza techniques, unlike other systems that try to say atemi is not aikido, or define it poorly, or don't teach it clearly. Tomiki did not stop with defining atemi as a posture. He also wrote about atemi's purpose: "Although the atemi-waza and kansetsu-waza can be viewed as techniques that can inflict a severe injury on an opponent, if we study the principles of the martial arts well, we realize that they are exquisite techniques for toppling (taosu) or controlling (osaeru) an opponent without necessarily harming him."

Gozo Shioda's explanation of atemi in Aikido Shugyo, "In Aikido, atemi is not limited to punching or kicking. Any part of the body can become a weapon for executing atemi. Some of you may have seen me in demonstrations use my back to repel an opponent rushing at me, or my shoulder to send my opponent flying as we pass each other. The reason these techniques work is that the contact point in itself becomes the atemi." Shioda's Yoshinkan has many explicit atemi as part of the kata.

Tomiki's atemi waza is ubiquitous. They are indeed 99% of aikido whether someone is getting hit by the movement, or responding to an attempted and prevented movement, or continuing on from the one movement. Shioda talked about 70%, but aigamaeate atemi waza became iriminage, and gyakugamae ate atemi waza became sokumen iriminage. Now Saito says kokyunage is the most common technique, but the movements are the same.

I think atemi has gone the way of aiki - a word we all use but not everyone understands and probably doesn't translate as cleanly across culture and time as we might like.