Not every restaurant is ran the same...and some will not like reading this, but there's also the tax free earnings angle. Cash is king. Employees are required to disclose tips and the generally accepted industry unsaid rule is report at least 10% and no one will question anything. If your credit card/large party gratuity exceeds that then you need to disclose it. Anything else on top of that (looks the other way). So, a server may make $1k in a given week, but if it's on $4500 in sales then their taxable income may be around $500 and the rest is under the table. This is a high turnover industry, but if you run a quality joint and you have an employee turning in those numbers you're more likely to retain them and that can only be good for business.
Is it a game? Absolutely. But remember those margins dkp mentioned. A manager/owner is aware this is happening, but outside of barring cash in the establishment there is no practical way to police it. Not doing anything about it keeps prices and wages down. It keeps employees motivated. I think if you take away the working for tips incentive the quality of service will deteriorate, which can only be a negative for the customer experience. And it's always easier to retain an existing customer than attract a new one.