I see you've never stabbed a guy.

Depending on the weapon, the amount of force behind it makes a definite difference. Bludgeoning is self-explanatory; more force applied equals more force transferred to the entire body of the enemy. Slashing weapons are also fairly straight-forward; the more strength behind a swing, the further through the body the sword will cleave before it stops.

Piercing is the only one that you may be able to have an argument for. Still, poking a hole two inches deep is a much smaller injury than pushing it all the way through.