"People like to think of themselves as sophisticates ... In the case of wine, they like the idea of buying something grown-up, with a relatively modest amount of alcohol."
But as Felix argues, there is a growing trend of wine producers deliberately understating the alcohol content on the labels. (The law permits a margin of error, and the wine producers exploit this.) There's an obvious motive for them - if consumers use the labels on the bottles as a guide to regulate their alcohol consumption, then this will result in people drinking more.
But why would the wine producers want to put more alcohol into the wine in the first place, and then lie to the consumers about it? This only makes commercial sense if this is what a significant number of consumers really (unconsciously) want.
As Felix concludes, consumers love to be lied to.
Felix Salmon, Why is wine getting hotter? (Reuters, 21 June 2011)