Restaurants are exempt from paying servers the minimum wage all other employers must meet. So it’s understood that their income will come primarily from tips.
U.S. restaurants are de facto separating food and service costs and counting on customers to tip servers enough to keep them in the job. In most cases, the tip amount is merely suggested up until a certain party size (usually 6) and then added to the check as an automatic gratuity. If tips were intended to be a gift for extraordinary service, this wouldn’t be done.
Rick Bayless, who owns several Chicago restaurants (and Frontera Cocina in DS) now adds a 20% “service charge” to all checks at his Chicago restaurants regardless of party size. It’s stated on the bill which also says “feel free to leave more if you enjoyed the service.”
Like it or not, tips are expected in our system and not treated by the restaurants, minimum wage laws or IRS regulations as gifts. It’s fine with me if people don’t like this and think the system should be different as long as they go along with the current one until changes occur.
The upside to tipping is that it does in fact encourage servers to go the extra mile in hopes of receiving a generous gratuity. I’ve heard many people say the service here is better than in countries where servers don’t rely on trips.
Whatever your thoughts on it, tips in the current system aren’t voluntary gifts to supplement a server’s income. They are the income.