Mary Barra was named the first-ever female CEO at General Motors, the second largest automaker worldwide, a month ago and has just been named the most powerful woman in business by Fortune magazine, ahead of Ginny Rometti, chairman (sic!) and CEO of IBM, and Indra Nooyi, CEO of Pepsi. Ms. Barra's appointment was celebrated as a milestone in equality. But it turns out that (unless GM hits performance targets) Ms. Barra earns just half of what her predecessor made as GM's CEO in guaranteed compensation. Is that fair? Unfair? Or unimportant?