4 down vote Here is Nicolas Brody's (Damian Lewis) answer on it -
Q. Why does the wife call him Brody? A. [Laughs] Morena’s been asking that all season. “Why don’t I call him Nick?” I’m a boarding-school-educated Brit so people have been calling me by my last name forever. So it doesn’t seem that weird to me. I think the writers see it as a term of endearment. (sOURCE:/
www.nytimes.com)By the way, it's very common for military wives to call their husband by their last name.