Re: Why do we use so much grappling in Aikido?
Well as it pertains to so much "grabbing" in aikido (without getting caught up in the semantics of what grappling is or isn't):
Grabbing techniques is a great way to begin learning techniques b/c one doesn't have to worry about intercepting an attack...the person has already grabbed (ok, this isn't for everybody...my style usually practices that they guy or gal has already grabbed you before you start technique). So this body to body connection has already been made, thus making it "easier" to some extent. Well, simpler, not easier.
Aikido is derived from Aikijujustsu, which is basically derived from what I call a form of Samurai Line training (what the US Marine Corps used to call hand to hand combat for the battlefield). Since samurai wore armor, kicking and punching were more or less worthless. Thus techniques that focused on manipulating the weak parts of the armor (ie, joints) was focused on (terrible grammar, sorry). The focus most groups do on open-hand to weapon combat is also a derivative of the idea that a warrior could lose/break a weapon and need to defend against armed attack.
At least that's pretty much what I would say if asked that questions on the koto shitsumon portion of a test.