I assume Peter is talking about Shodokan Hombu. Certainly people who go to practice at the hombu dojo of any style should be serious enough about aikido to practice intensively and usually with the purpose of getting their shodan asap, especially with the high cost of training and also living in Japan.
But of course at local dojos, ordinary people looking for some exercice, or having seen Seagal sensei movies... come to try aikido for a while, but drop out later for whatever reason (many actually, like not getting shodan in 1 year, discovering that aikido is not as soft as advertised, or too soft, or difficult to master...etc.etc.).
I have read statistics somewhere that only about 1% do make it to shodan generally.
As those who work so hard to get their shodan, and feel that they have finally achieved what they were looking for, and quit thereafter, probably have never understood what aikido is all about, so, "bon debarras"!