Gratuity act-applicability

Gratuity Act states that Employee as per Sec2(e) does not include "any such person who holds a post under the Centarl Government or a State Government"

My father is a Central govt. employee & he is entitled to gratuity,on the other hand  my sister is  a State govt employee but she is not entitled to gratuity.

My query is,when Gratuity Act doesnt apply to any central and state govt employees,why my father is entitled to it?& if he is ,why not my sister?