I own a restaurant and can tell you that waiting on tables is darn hard work. The pay can be very good if the server is really good, but there are always those people who refuse to tip, or tip very little.
It doesn't matter to me whether tipping is the cusom or not. Tipping is just one way of compensating the employee. If tipping were not the custom their salaries would be built into the price of the product. The customer always pays for the employee's wages. The hammer you buy at the hardware store has the employee's wages built into the price.
The television you buy at the store has the employee's wages built in too.
So when you go into the restaurant and buy a $10 dinner the wages are not built in. If tipping were not the custom that dinner would be $12 for the other $2 to go into the server's salary. Get a grip on reality people, you always pay for the salary, in one form or another.