In the US, you are allowed to pay servers less than the normal minimum wage if they are taking tips to bring their wages up to the minimum. This is also why US tips are usually 15-20% of the meal -- you are essentially directly paying the waitstaff for their service. (I also suspect if diners knew everyone on staff was making well above minimum wage, tips would be lower, since they can be... well, tips, instead of 'please do not starve' money.)

Granted, $8 an hour is still below a living wage for much of the country.