My point is that these days, especially accounting for assortive mating, a married person is better seen as having someone to support him or her, not as needing to support someone else.

Your roommate isn't going to pay for your food and rent. Your spouse will. Moreover, old married people are much more likely to have assets to draw on if someone is unemployed than single people. And while they may have higher expenses, a lot of those (like child care) disappear when one person is unemployed.

Just looking at my friends, very few of my single friends could tolerate loosing their jobs as well as my married friends. That includes older couples I know with kids.