When you talk about wine, it's common to refer to the year of harvesting the fruit.
Different fruit varieties are better some years than others. So when Michael Moore says "what's a good year for merlot?" He's asking in which year was the grape variety (merlot) considered at it's best.
So, the response might be 'for merlot, 1997 was an excellent year for a Marlborough merlot'. When the season was perfect for growing that particular grape variety.
Of course the same grape variety, is grown in different regions of the globe. Normally in a temperate climate like Chile, France, California, Australia, and where I'm from New Zealand. So, a better question might be "what's a good year for a Californian merlot". Marlborough is a wine growing area in New Zealand
http://www.wine-marlborough.co.nz/home.htm.
I hope this is helpful