The first time I ever gave a talk about singles to a big audience, a man came up to me afterwards and told me that he has a happily single sister, but his mother still prays every night that she will find a husband. He wasn't the first to tell me a story like that.
I think the assumption that everyone is heterosexual is going to fall before the assumption that everyone wants to get married. The former is already limping. The ongoing and very salient debate over same-sex marriage, together with other high-profile discussions and projects, such as Dan Savage's "It Gets Better" campaign, have given pause to at least some people about to ask a woman if she has a special man in her life, or a man if he has a wife. They realize that a person's romantic partner could be of the same sex, and occasionally adjust their queries accordingly. But rarely does it occur to the questioners that nabbing a romantic partner of any variety may not be every person's goal.
By aiming conversational volleys in the same predictable direction every time, our partners in small talk miss out on all of the other big things going on in our lives - all of our other interests, passions, and pursuits. We need to be ready to volunteer our own stories, lest we be altercast into caricatures of ourselves.