Not so, actually, according to the requirements that Dan cited. Yes, I was surprised too. Maybe that reference is incorrect?
Yes I was being USAF myopic. I just also looked at "Aikido and the Dynamic Sphere" which lists the requirements for testing at hombu and NY Aikikai as of 1964 and 5 respectively (p.37-38).
The Hombu ( October 1964) are: 5th Kyu - 40 hrs, 4th - 40 hrs, 3rd - 30 hrs, 2nd - 60 hrs, 1st - 60 hrs, Shodan ( none listed, but the technique required is the same as 1st kyu so if we keep the hour requirement the same we get 290.
The NY Aikikai (Spring 1965) are: 5th Kyu - 60 hours, 4th - 60 hrs, 3rd - 60, 2nd - 60, 1st - 90, Shodan 150. We get a total of 480.
So it is interesting that the requirements have inflated over the years.