Re: The shoulder grab - where does this come from
The grab and punch is a common explanation for it that I've heard, but I feel that's our answer to why and not the answer.
We do both the push to the shoulder and the lapel grab under the name katatori, just depends on who you're working with and how they choose to do it.
my own more recent explanation for the modern impracticality of the "attacks" in aikido is that they are meant to be little more than exchanges of force designed to test/reinforce proper body structure and stability and your ability to negate/absorb/redirect that force acting on your body on your way to breaking uke's balance and throwing or controlling them. Basically like paired exercises rather than some sort of simulated confrontation or fight.