Actually, that argument's a bit weak, since there is the Block skill which will be the most useful to shield-bearing warriors (which means upping two skills). Anyways I'm not assuming that it's 100% Dual-Wield, I'm just saying it's a very likely candidate and I can't think of anything better.
It's not weak at all. You can still block whether it's one ,one handed weapon,two,one handed weapons,or a two handed weapon.
A one handed weapon ,requires one hand,even if you are holding one in each hand,it's still a one handed skill.
Two handed weapons are two handed for a reason,weight,length,style etc.
Yes blocking with a shield is more effective,but you can block with two,one handed swords too.
I believe it will be a perk or be there by default. Same with spells.
Just my view