I think there are two "benefits" to businesses that engage in this behavior. The first you alluded to - the business owner can decide whether he or she passes all, some, or none of the fees collected to employees.

The second is that it allows them to charge higher costs than shown on their menu. In other words, this is a classic "bait and switch" tactic. You can see online the prices quoted for any menu item, but when it comes time to pay, suddenly you're paying significantly more than you rightfully expected.

Because of this, I don't go back to any restaurant that charges anything more than what's on their menu (plus tax, which in other countries is included in menu prices, but that's a whole 'nother story).

If the owner cares so much about his or her employees, he or she should put on the menu the prices needed to be able to provide a livable wage plus reasonable benefits to employees.