If it's mentioned up front and fixed then it's fine. One way or another the restaurant needs to cover it's costs and it's either done via inflating the price of the food or a fixed service fee.
What I hate is a discretionary tip suggestion because suddenly I'm made to be responsible for how much the staff get.
I'm going to take a swing at the moon reflects a relatively uniform spectrum of light from the sun but our varied atmospheric conditions can alter the refraction of that light.