The incident Robert describes is from a dan test. The person testing was obviously not comfortable with the atemi waza aspect and appears to have little instruction in applying atemi waza. She seemed to be mechanically applying strikes-almost like well I'm supposed to atemi her so she would stick her fist out.
This is not a good example of how to deliver atemi waza. I do place considerable importance on atemi as it is my believe that the training in the art aspect and street capabilities are defined by the suki (openings) for atemi waza and atemi is necessary in a combative situation to make the technique street effective in most cases.
Not only is the atemi necessary but it needs to be delivered to appropriate spots-ie. vital points (as the definition of atemi provided in doshu's new book). Striking someone on the arm has little effect if not in the right spot. However, a strike to the right acupuncture or nerve point will help position the attacker for delivery of a technique and also help the tori to control the aggression of the attack.
Most aikido training in atemi is weak at best. The example Robert cited (I saw the tape and was on the test committee) was primarily one where the tori had little formal training in delivering proper atemi (IMHO).