Yes, this is a fantasy game. But just because it's one doesn't mean it doesn't have to feel real.
By your logic we should fly into battle on huge chickens with bunny heads, because hey magic isn't real either.
Wooooow...
That's just...a terrible, terrible extrapolation of the argument.
You argue that dual-weilding is unrealistic when it isn't and is used in reality in many applications but that doesn't 'feel real' to you? I think research is something that anyone should do about this, before assuming something is unrealistic. Magic does not actually exist as far as we know, however it can be treated in a believable manner. The same applies to anything in a fantasy setting. If, say, a wiry Dunmer were able to effectively wield two massive warhammers in battle and trounce anyone in their path without breaking a sweat, that would be unbelievable (see WoW), but two daggers, a long-sword and handaxe, a staff and mace, are all believable.
However, I think we'll find that dual-wielding is not simply a damage multiplier but will reduce defensive capabilities as well, so you may be able to do more damage, but you won't be as efficient at blocking. It can be balanced. On top of that, you don't have to make use of it in your game, at all, and if you come across an NPC dual-wielding you can laugh at them as you smash their skull in with your two-handed warhammer. Dual wielding may not be incredibly common, and whether you 'feel' it is realistic or not is irrelevant to the fact that it is 'real.'
http://en.wikipedia.org/wiki/Sai_%28weapon%29
http://en.wikipedia.org/wiki/Butterfly_sword