I always tip on wine, don't get me wrong, but its ok to tip on corkage too. Some times I feel like I have been tipping wrong, when I feel like I can just tip the bartender more sometimes.
It's true that is part of my meal but are you really telling me that if I order a 100.00 dollar bottle of wine or a 15.00 dollar wine I should tip respectfully when they just open and pour my first glass?