Or is fists considered light weapons?

Vulpes

Yes, fists are 'light' weapons, but this has no game application as you are not allowed to dual wield fists in IWD2. Actually, monks can't dual wield fists in p&p, though other characters can. Monks are assumed to already be 'dual wielding' as part of their increased attack and damage rates when fighting unarmed.

Weapon focus/finesse/specialization in unarmed does exist in the p&p game, but wasn't implemented in IWD2. I think the reason is because they don't have a 'fist' weapon proficiency class in the game and didn't want to add it just for this purpose.

While monk players would like to use Weapon Finesse and Weapon focus for unarmed attacks, the game designers felt the monks' unarmed capabilities were sufficient without this additional assistance.

Weapon specialization would obviously only apply to monks that have 4 levels of fighter as well. Not that many in the overall scheme of things, since monks are *very* level dependent for their abilities. Dual classing when a monk isn't a very cost effective idea, assuming you intend to actually act as a monk. A few levels of monk can make a nice set of bonuses for another type of character, though. But such characters likely wouldn't be doing the unarmed thing anyway. They are probably spellcasters. :)