By Lenn Thompson, Executive Editor Maybe it's because I work in marketing and understand why a winery would want to create of differentiation and exclusivity — and often charge more for it — but I often find myself taking a "prove that it matters" stance when I see a wine labeled as a single-vineyard one. I'm not saying that single-vineyard labeling is the same as "reserve" labeling. I'm just saying I'm skeptical and need to be convinced. Luckily, I'm convinced more often than not in the Finger Lakes. As Evan wrote about over a year ago, several wineries there are…