Basia, "most cases" refers to current Hombu AIkikai requirements, as well as other aikido organizations, two of which I'm adding here. The USAF's numbers were the same in the 60's, and I've shown earlier in this topic how their requirements have hyper-inflated over the years. It's as if USAF is asking people to put in the time and money that in "most cases" around the world would get people into a master's or part way to a PhD, and giving them a bachelor's.
That might have some merit if USAF was turning out remarkable shodans, but they're not. I've had the opportunity to train aikido with many people from many organizations and countries, and I've found - on average - a student that's been in a hakama since 3rd kyu and reaches shodan around the three year mark, has a better overall proficiency and level of understanding of aikido than most USAF shodans I've trained with.
I think the argument could be made, that drawing out the time to shodan - and in some cases, wearing of a hakama - too much can actually stunt growth - often dramatically. And it also turns the idea of a shodan - which is really the beginning of the school - into a much bigger carrot than it should be. Grades and requirements can be used as effective learning instruments and standards, but they can also be misused.
ASU requirements: shodan 39 months, 510 hours
Tomiki: shodan 340 hours