I had a chance to talk to my chief instructor Eley Sensei about the Ki Society tagi. He noted that the strikes in the taigi were large, observable strikes designed to get a reaction from the uke. Actual atemi is shorter and should not be noticed until it lands. So perhaps that is why tagi "atemi" can be called "strong leads".
He also noted that there was a definite change from Aiki Budo to Aikido. The pre-WWII art had atemi while the post-WWII art didn't emphasize atemi and took it out of the teaching curriculum. You might assume that this was the founder's doing. Since K. Tohei mentioned that atemi got in the way with learning a technique's movement, you might also assume that this was a reflection of the founder's thoughts.
In the above case, I am using atemi as a physical strike. It is not a kiai or extension of ki or focusing your energy, although I can see how it can be interpeted that way.