Well, telling you the fact, prenuptial agreements are not just for the rich. However, they are often used to protect the assets of the wealthy; couples of more modest means are increasingly turning to them for their own purposes. For instance, a couple who is getting married with children from prior marriages may use a prenup to spell out what will happen to their property when they die, so that they can pass on separate property to their children.
Thus, without a pre-nuptial agreement, a surviving spouse might have the right to claim a large portion of the other spouse's property, leaving much less for the kids from prior marriage.