We were told by a waiter who worked at one of the chains that they get automatically taxed 8% of whatever bills they have dealt with. That means that if you don't leave a tip for whatever reason, they will be charged 8% of your bill in any case, so if you leave 10%, they will only receive 2%. That is why for the most part, service is pretty reasonable or they would be out of pocket. It sometimes is not the fault of the waiting staff if the food is poorly turned out, but they suffer the consequences. That is one of the reasons that they get paid a very low wage as they are expected to get income from the tips.