My staff get 10:50 an hour. However they aren't working full time for me as we are only open at weekends so they all work elsewhere too.
The service charge or the tip in cash is an accepted way to recognise the staff for going the extra mile to make your experience memorable and making you feel really special. Most people will tip a taxi driver just for conveying them from A to B without a second thought, in fact they expect it with the exception of Uber drivers. Most workers do their job within the job description to the best of their ability. Technically my staff's job is to greet you, take you to a table, furnish you with a menu, water and snacks, take your order and deliver your drinks. If that was all they did I don't think we'd be very busy and few would return for a second time. They don't get paid for having the conversation with you about your day, your mood, your holidays, your kids, etc or for making recommendations on where to eat after your drinks, making reservations for you, calling taxis, finding out about your drinking style and recommending drinks you'll like when there is nothing you fancy on the menu.
Service staff are a special case. When they go above and beyond the call of duty they are not just doing their job : they are making you feel special and making your evening better in a huge way.
All sorts of workers get "tips". My mum used to tip the bin men at Christmas! Many get a Christmas bonus from their employer which is payable because he has charged you, the customer, a little more than he absolutely needed to to make a profit. Kids give teachers presents at Christmas and when they leave school, or when the teacher retires. Anyone in a sales job is well-used to target-related bonuses for extra effort. Many executives get "perks" like cars, phones, foreign holidays. Politicians get loads of extras above and beyond their generous salaries.
My staff earn every penny of their tips, unlike many workers who just expect bonuses to be paid every year regardless of their personal input.
My point is that you are paying service charges all the time, but in some cases the employees will only get a small percentage of it, upper management will take a share too and you will never know if your great online review was recognised for that employee or not. The service charge system is open and closely regulated to keep it in the hands of the workers themselves, as are tips when properly organised.
I can't speak for the USA but their service charges seem to be around 20% in my industry. You do generally get AMAZING service in the US though.
Simon