That's a pretty good question, we know we can dual wield, or use a one handed weapon with a shield, but what about just using a one handed weapon without anything in the other hand? It could well be that there will really be no benefit to doing so, a problem which past games had too, honestly, it's nice that dual wielding provides an alternative for players who want to use one handed weapons but don't want to use a shield, but it still doesn't adress specifically what players who want one weapon and only one should do. My suggestion would be to give some sort of bonus only available when using one handed weapons with nothing in the off hand, but I'm not sure what the best option would be for that.
The benefit for players that want to use only one weapon is that they can have a spell equipped in the off hand.
2hand weapon--slower, high level of damage
Dual wield--faster, lower damage
Sword+Shield--lower damage, strong defense
Sword + Spell---lower damage, secondary magic effect
Shield + Shield---no damage, strongest defense
Spell + Spell--lots of options
I believe the confusion about the blocking mechanics is just that...confusion. We will be able to block with all weapon combos. I really don't see anything wrong with the system as set up. Each weapon combo has advantages and disadvantages.