Is there such thing as a "man" in a relationship? I say no, but what do you think?

I've always thought that even though one woman may be more "butch" or "masculine" than the other, in a relationship, that this does not necessarily mean that person is the "man" in the relationship. Most people have argued with me otherwise. For example. Ellen and Portia, They would label Ellen as the "man" and Portia as the "woman" in their relationship. I don't think such labels are necessary. Thoughts. Opinions. Questions. Comments. Thanks :)