Hi Kevin, I'm with Jim on this, especially where a grab is concerned - if someone grabs you I think you would be crazy NOT to assume there is a bottle, knife, glass in the other hand.
To train for years to defend against a grab with an assumption that there is not a weapon in the other hand simply 'makes no sense' (to use your words).
We always train with the assumption that the attacker might have a weapon, and it might not be in the hand they hit/grab you with, beginners included. They seem to cope somehow
If you want aikido to be martially effective, how could you do otherwise without kidding yourself?