(Reuters) - Just as Amazon revolutionized the way books are sold and Groupon has conditioned shoppers to expect daily deals on services and foods, a cluster of websites have upended the stodgy world of wine. At least a half-dozen online websites in the United States, a few in Britain and Australia and one or two in France promote wines, sometimes for as much as 60 percent less than retail, using social media. But are they really good deals?