Well, in that specific case, we had a full meal, were there for over five hours, and drank over a dozen bottles of $75 wine. That being said, it was a very GOOD restaurant, with the service always filling waters, getting fresh bread, etc. We tipped on the whole bill, but I wouldn't consider it average.
Considering your mom's opinion, though, I have to disagree, since often the bartender(s) get a cut of the alcohol tab, therefore lowering your actual server's tip.
-MattL ---
"An intellectual snob is someone who can listen to the William Tell Overture and not think of The Lone Ranger." -- Dan Rather