Because in the game it do not, the attack or defend just the same,for example 20 spearman would defend better than 10 spearman, you can attack with 20 warriors to 1 musketman and lose 10 times, some times just lowering the hitpoints, but in a real fight the warriors would surround the musketman and easely defit them.
So when you out number the enemy you should recive a bonus, like 2 to 1 a 25% bonus, 3/1 35%, 4/1 40% or something like, why wont some one post to express their opinion or make a suggestion?