This is not true.
Earning of the industry is decided by the single factor called Crowd Pulling Capability. So if writer has better crowd pulling then he/she will get the higher money, if actress has better crowd pulling then she will get more money then male counter part.
Few examples -
Salim/Javed used to charge more money at peak then leading male actor.
Madhuri got more money then Salman for Hum AAPKE HAIN KUAN
Kangana got more then Madhawan for TANU WETS MANU - 2