The method of growing, soil or hydro, do not necessarily affect the potency of the plant. However, certain methods are more conducive to sucess than others. For example, we know that more oxegent to the roots of a plant the better it does, but we also know that certain micro-organisms can affect plant nutrient uptake. Hydroponic growing is simply simpler to control, and more likely to be free of disease if done right. And if the plant isn't wasting energy dealing with stresses, then it will probably result in more effecient and productive use toward growth and development.