She owns her own production company. Owns her own show so she's not just taking in a paycheck. That's why she's worth so much money.
Because they touch everyone with the feeling of reality and honesty that she tries to emulate within each of her shows. She only tries to understand the truth about life and what others are doing with theirs.
It just goes to show what can be accomplished when racism and sexism are set aside. (Not that Oprah hasn't experienced racism and sexism and not that she isn't an exceptional person in her own right - but a hundred years ago a black person or a woman of any colour could not have gotten where she has.)