I read the Lead Blog post: Simplicity.
Simplicity means the achievement of maximum effect with minimal means. – Dr. Koichi Kawana
I though that was the definition of Effectiveness.
I think that a better definition is: Clarity, Precision, and Ease
Once you are clear, precise and easy, you will probably be effective. That is what makes simplicity so hard, that is why we spend hours and hours discussing how to make our products simple.