If the wife works full time like the husband does, spends 12 hours outside of the house making her career and not taking care of the home and family any more than the husband does, then why would she not be expected to pitch in for the bills?
Its not the "why would not" or "why should not" etc, its the question is "if she is REQUIRED". Sure if she wants to pitch in with her contribution that will be good but she is not REQUIRED to do that.