My ex-H and I had a version of this dynamic. I was busy overfunctioning while he was busy being the rebellious/bad son. To this day he interacts with me this same way.
My present H was actually attracted to me because of my maternal qualities. I strenously resist when he refers to me as "Mom". However, I still sometimes wonder if this dynamic affects us too. Maybe in our case it is less a Mom/son and more a Madonna/Whore issue.
SuperDave,
I am very sorry that your W would express such a hurtful thing to you. Is it really genuine or is she just protecting herself/insulating herself from her own failure to engage in the M by saying "well I haven't fancied him for 26 years anyway." If it is an accurate statement then that is a bitter pill to swallow. If she's just hiding behind it then there is hope.