When you have this debate with servers that work in restaurants (particularly those that are slightly above your conventional Jack Astor's, Boston Pizzas...by food price), they are always quick to point out, their minimum wage is different from staff at Tim Horton's, etc. Well than go there and make the increased minimum wage then.
But who are we kidding. We all know they are raking in close to $20/hr with tips or more. Let's not kidd ourselves as to whether all of that is disclosed for income tax either.
And as other posters above have suggested, % is so outdated within the concept of tipping. Sometimes I join my friends late, and all I get is a soft drink, but I'll ask for a couple of refills, which actually results in more work for the wait staff than bringing a meal, with one check-in during the meal. If I gave 15-20% on my tab, it would be like $0.50. That's pathetic! So I'll usually give $1.50-$2. On the flipside, when I'm having a meal, I'm usually very low maintenance. They bring the meal, they have one "how's everything" check-in, clean-up dishes and ask if interested in desserts, and bring the bill. Whether I ordered a $30 dish or $15 salad or $10 appetizer in the same restaurant, the work is the same, but the tip is so drastically different on a %-basis.