That's true, most Indian restaurants do not allow the waiters to keep the tip. In regular American restaurant (means almost all non-Indian restaurants), waiters get a base pay of around $2.75 per hour. But they are allowed to keep the tips, of course minus certain percentage that goes to bar, bus boys, taxes, etc. The final tally for the waiter's wage comes to $10 to $20 per hour in average restaurants. The owners of Indian restaurants just provide salary to their workers, usually 3 to 6 hundred dollars and most of the time that does not sum up to even minimum wage level. They can do this because most of the workers are not documented. Call it exploitation or the sway of invisible hand (remember Adam Smith?). So, I would give cash tip directly to the waiter if you like his or her service, preferably away from the manager/owner's sight.