Nicely said!
So spell casting is dependent on what is occupying your hand slots at that time. *tick*
If both hand slots are occupied you can't cast (as far as we know so far)
I am aware that the loss of limbs will not occur in Skyrim, but I am merly pointing out the flaw in restricting the use of magic to the state of ones hands. What if someone had no hands. It's a reasoning process called deduction:
PCs require a free hand to cast spells
PC has no hands
PC can't cast spells
So who cares right cause lose of limbs is not in. It is a simple observation, that in other fantasy worlds would be a consideration, as lose of limbs is common in blade based warfare. (and yes, you would be scrwed without hands in Skyrim, but what about if you've lost one hand?). Who cares tho, just a thought.