Carrie,
I think it's that you, for lack of a better word, simply knew that while you could be your mother's caregiver, simply because you are a wife, does not directly mean you could be a caregiver to your husband. Completely different dynamics.
I remember when taking care of my mom, the hospice nurse would come in, I would introduce myself as her daughter, and also state that I am an RN. One replied "well what am I doing here?" I was too stunned to reply "because this is my mother!" Simply because I'm a nurse doesn't mean I will not need someone else to ASSIST me in her care.
I just see it as a different dynamic of caring for your mother, than your husband.
Hope that helps you.