hi, i'm new to this myself but im'm pretty sure that you can also have an organic hydro grow assuming that you mean't you have an organic soil grow. using molasses as a nutrient in your hydro system. also for a 1-3 plant system can prob set you back anywhere from around $50-100+ if you do it yourself and hundreds of dollars the more specialized equipment you get from hydro shops and what not. but to some what anser your question on why hydros better to the best of my knowledge is that more O2 get to the plants root therefor enriching it also since it is suspended directly into a nutrient solution it is capable of absorbing them at a higher than normal rate. i'm sure theres other reason but i'm sure thats the basic portion of it.
FedaykiN,
Peace