I agree. In fact, why not go a little further and make everything cost 10% more. Then, the customer knows up front exactly what the meal will cost. However the restaurant wants to split the revenue of the final check is up to the restaurant.
I frequented a restaurant that did the latter. The problem was that they did a bad job of advertising the fact & would sometimes go as far as to not give an itemized check. I personally felt like I was being duped. This led to customers tipping on top on a tip & when customers found out, there was a lot of rage on Yelp et al. They repealed the auto gratuity.
Point is, if you are going to do this be loud and clear about it.