in many cases service industry workers have suppressed wages due to the inferred gratuity income.
servers in Georgia resturants more often than not are making about $2.00/hr in pay. its legal and the gratuity inference is why.
I tip transport drivers because they have my personal safety in their hands.
and they handle my bags.
and to engender good will and loyalty to their duties.....that may not directly benefit me.....but perhaps the next crew down the line that driver may go the extra mile for...because he remembers I didn't stiff him on a $5 tip.