It doesn't always happen. There's a place in downtown ROC that's a great place to grab "plates" (ahh how I miss those) after a hard night of drinking but the owner is notorious for pulling fast ones. I've seen him pocket tips many of times and had learned to hand the tip directly to the waitress before paying up front.
Those girls in there earn their money - its a rough drunk crowd late-night and have to put up with a LOT of s%@!.
-JC