At least in D2:ED, when duel wielding the stats displayed the average damage of the two weapons. I never tried duel wielding in the demo, and haven't started a new character yet in the full game.
One thing I did notice in the demo, with a bow doing 1-3 damage equipped, in the stats if I had any filled equipment slot selected (by the character model) the damage was listed as 1-3. However, if I selected a slot with nothing equipped (like the helmet), the damage changed to 2-2.
