Many hydroponic grow systems do not use any media at all (for example Gro-Tanks), the grow systems that do use media are not using the media to supply nutrients, the job of the media is to support the plant physically (hold it upright) and to perhaps hold onto some of the nutrient solution until the next feed.
Hydroponic media are porous, light, and coarse, which allows oxygen and nutrient solution easy access to the plants roots.