But usually in PC games you use the left mouse button for items on the right hand. FPS games usually have all the weapons in the right side of the screen and same goes for Skyrim probably if you just use a shield in your left hand and a sword in your right hand. I mean you will still use the LMB for the sword (which is actually in your right hand). Will you not?
What happens if you get 2 swords or 2 spells. Will the mouse buttons suddenly be reversed or will you use the left button for the right hand and the right button for the left hand?
The consoles don't have this problem, because usually the right trigger is used for shooting (in FPS) and so on.