I liked this quote from Michael over at You Can Know God:
Waitresses make $1.50 an hour and a share of the tips, bringing them up to a “normal” hourly wage. But the tip is arbitrary and changes from night to night. That defeats the intention of a gratuity, which was to give the server a little something extra. A restaurant doesn’t pay the employee the fair wage, but counts on the generosity of the patrons to make up for their low wages. What other industry operates on this kind of pay scale? What if we lowered the salary of other people and made them count on tips to make up the difference? I think this might work for politicians.
See his full post here