I believe the quote you are refering to is found in John Stevens' "The Secrets Of Aikido" (Shambala Publications, 1993), I forget the page exactly, wherein O'Sensei went into the dojo to teach some techniques. However, all the techniques he taught appeared to be Ikkyo.
One student said, "Sensei, what is the difference between all those techniques? They seemed the same."
O'Sensei immediately thundered back, "When you see the difference between these techniques you will have understood Aikido!"
I'm not sure he meant it literally, but rather when you learn to look BETWEEN the techniques (to the essence) you will have mastered Aikido. I could be very wrong though, so don't take my word for it.
In any case, Ikkyo is very important in Aikido, because it is one of the first techniques taught, as well as one of the simplest. Let's remember, however, that SIMPLE doesn't necessarily mean EASY or easy to master. It is also one of the most effective takedowns. Ask any cop.
Some books you might want to check out: Saotome Sensei's "Principles of Aikido" and "Aikido and the Harmony of Nature"; John Stevens' "The Essence of Aikido" and "The Secrets of Aikido" as well as his biography of O'Sensei; Dosshu Kisshomaru Ueshiba's "The Spirit of Aikido". Ask your instructors, they'll point you in the right direction.
Hope this helps.