yes you are right. there are always "anomalies". we have all heard the story of the the waiter who made more than the owner of the company, blah blah.
the reason those of us in working in "the industry" get upset is this.
people read things on message boards. or SKIM message boards and dont' read everything. they see "Oh! delivery guys get $10.25 and hour"! _"Oh, they make more than IT guys!"
that's all it takes for for cheap people to justify giving a guy a lousy buck for a tip. "I saw it on the internet! they get blah blah an hour and don't use their own cars!.. they make more than I do!"
PEOPLE.. someone is bringing your hot meal to your door.. standing there while you take forever to answer the door.
probably act surprised that they are there!!!!! "gee? so soon? wow.. we are in the middle of a movie.. can you wait a minute?/ um.. honey. do you have money for the pizza???" .....(cause we are SO surprised that we ordered a pizza and it's here...

) ok, it's 23.50 ... here's $25.00. sorry, dont' have any other change.