I think tips in many places are slowly converging into something like a 20% commission paid by the consumer, thanks to restaurants including a suggested tip on the screen or receipt, and bars automatically charging a 20% tip if you don't explicitly close your tab.

I hadn't thought of this before, but keeping tips as formally selected and paid for by the consumer may help the restaurant with liability issues where alcohol is involved. Paying servers and bartenders a direct sales commission might become an issue in court if a customer is overserved.