If you buy a cross section of wines from a given producer and have a hard time deciding which one you like the most, welcome to the club. In today's world, with the emphasis on single vineyards, many wineries produce a handful or two of wines made from the same grape and vinified in the same way, yet grown in different locations. That is the essence of terroir—letting a site express itself through the wine. It's the ultimate in finding a niche and, in turn, niche marketing. Wine Spectator's James Laube explains.