It might not be applicable to the UK, as someone else pointed out, but this is absolutely the case in the US. On a good night, a server might make several times more than their hourly wages in tips alone. I've known plenty of people that worked as wait staff at a restaurant that liked the tipping system because thanks to tipping their wages were several times higher than minimum wage. Most of them would have rather had a slow night once in a while rather than give up the tipping because of how much they made thanks to tipping.