They increase portion size just a bit to make sure no customer ever is left wanting or questioning the value. They terminate servers who shouldn't be servers, and work to support those that should. Above all else, they make sure that every customer gets what they want out of their dining experience. A lot of independents never get this concept, and never reap the rewards this business can bring. Chains on the other hand understand this perfectly clearly, and insist all locations work towards these goals of customer satisfaction.
People hate surprises.
Virtually all chains insist on strict menu guideline adherence, and very physical location management. And because they keep bringing customers back with appealing decor, good food, and reasonable service a good part of the time, they have the money for those glitzy advertising campaigns. And as a mystery shopper, I can absolutely guarantee you that unless you are taking off those blinders and getting your customers point of view, you're likely missing the boat by a huge margin. The key, once again, is to know what your customers or potential customers want, are willing to do to get it, and what they are willing to pay for it. The most professional realize that that answer is always a moving target.