ANSWER
Costco. In 2002 the Seattle based company became the largest wine retailer in the US. According the Seattle Post-Intelligencer, Costco's Global Wine Director David Andrew is now "quite possibly the most powerful wine buyer in the country".
Other wine trivia: As several readers pointed out, Ernest & Julio Gallo is the largest wine producer in the US. And the largest single wine store in the world is Sam's Wine & Spirits of Chicago. The 33,000 square foot store stocks over 20,000 wines, spirits, beers, gourmet food items, and cigars.
WHO GOT IT RIGHT: Marc Quinlivan, Robin Campbell, Marika Thiessen, and Bob Milligan.
