I'LL TOAST TO THAT! a study (pdf) shows that it's not just moderate drinkers: it's also heavy drinkers who outlive teetotalers:

But why would abstaining from alcohol lead to a shorter life? It's true that those who abstain from alcohol tend to be from lower socioeconomic classes, since drinking can be expensive. And people of lower socioeconomic status have more life stressors — job and child-care worries that might not only keep them from the bottle but also cause stress-related illnesses over long periods. (They also don't get the stress-reducing benefits of a drink or two after work.)

But even after controlling for nearly all imaginable variables — socioeconomic status, level of physical activity, number of close friends, quality of social support and so on — the researchers (a six-member team led by psychologist Charles Holahan of the University of Texas at Austin) found that over a 20-year period, mortality rates were highest for those who had never been drinkers, second-highest for heavy drinkers and lowest for moderate drinkers.

[...] Even though heavy drinking is associated with higher risk for cirrhosis and several types of cancer (particularly cancers in the mouth and esophagus), heavy drinkers are less likely to die than people who have never drunk. One important reason is that alcohol lubricates so many social interactions, and social interactions are vital for maintaining mental and physical health.

¡Salud!