Strength is the most useless stat actually. All classes have one specific stat that adds attack (basically adds .5% damage per level of the attribute), and adds to one other offensive stat. In the case of strength, this is guard damage. It may be more useful at higher difficulties, but on normal not a lot of enemies use guard, and guard does not add a lot of hit points in any case.
But for all classes, willpower also adds the .5% attack per level, plus magic defense. On harder difficulties this is much more useful than guard damage. So willpower is actually a better stat than strength for warriors to add damage.
The attack percentage is just a multiplier on your base damage in the damage calculation, it doesn't matter what weapon does the damage. Here is the damage formula:
final_damage = (base_damage * rand(0.95 to 1.05) - armor) * (ability_multiplier) * (1 + critical_damage_bonus + flanking_bonus) * (1 + attack_bonus + damage_multiplier + type_bonus) * (1 - magic_resistance)
So you see "attack_bonus" is just part of a multiplier to increase damage. But do note that despite removing class restrictions, increasing dexterity will not increase attack for a mage wielding daggers. But magic or willpower will increase attack and apply to the damage the daggers do.
Here is a thread discussing mechanics if you want to check it out:
http://forum.bioware...mbat-mechanics/