This may be mentioned in one of the links, but here is a major problem with not tipping on alcohol, aside from established standards of etiquette.
At many places the server is required (or strongly encouraged) to give the bartender a portion of their alcohol sales. It may be 10% of their alcohol sales.
Say you order $500 of food and a $1000 bottle of wine. You tip $120...20% on the food, and $20 bucks for opening and pouring your bottle of wine.
The bartender will want to know where his $100 cut is for that bottle of wine, and they will have to work out some arrangement, or worst case scenario if the restaurant takes that money out automatically, the server would be left with $20 bucks.
But, as other posters have mentioned if you can afford the wine, you can afford the tip. As mentioned in a related post, I have some friends at Jeff Rubys and sometimes these athletes or celebrities will come in and order 3 or 4 bottles of Cristal just to start the dinner. Thats when the servers start frothing at the mouth because they know they've made several hundred bucks already on one table before dinner is even ordered!