Well... in the cannabis plants, the cannabinoids usually are in the acid form (THCA), which is not psychoactive. This THCA is transformed to THC by heating, or slowly, by itself, with the passing of the time. So, when you cure the cannabis, it gives the THCA enough time to it transform itself in THC, and thats why properly cured cannabis is more potent.
This process happens wherever there are cannabinoids, so it must work for hash too.