Having taken both Judo and Aikido, I think that the differnces in osae are there for very good reasons (in my limited experience). Judo tends to focus more on a sport aspect, which means a one-on-one confrontation with rules etc. Aikido(at least in my school) is taught as more of a self-defense method, which means the possibility of dealing with more than one attacker. Kesa gatame is great, but if a couple of guys try to grab it's really no good to hold one person down with it while the other kicks you.
It's always seemed to me that the pins in Aikido are there because:
A)They can be applied quickly
B)Most can be applied standing or kneeling.
C)All are very effective in actually injuring someone.
While I realize hurting someone is distasteful, and not at all desirable, if you get attacked by two or more people, well it's probably inevitable that you will hurt one if you wish to remain unharmed.
Just my two cents...