That's my point, the brochure makes a point of disclosing an automatic gratuity on out of pocket items and for parties of more then 5. A customer is entitled to rely on the terms of the plan, as described by Disney, in making their decision.
Subject to change doesn't allow a business to change the economic basis of the plan, by adding an extra charge. Nor would it allow Disney to change the plan to 2 quick service meals and one snack per day. Subject to change allows Disney to adjust the list of restaurants and to change which restaurants offer which meals.