goody613 – R’ M.M.Weiss mentioned this on one of his tapes. he provides an explanation as follows:
the work was distributed out in such a way that the women were given work more suitable for men and vice versa. So when we point to our wife it is because we are showing that they had the bitterness to a harsher degree and suffered these hardships and when we say maror zu, we remember this and point to the wife to show appreciation for all that she did and does for us.