Peter, while I'd quibble with your choices as examples of creative chefs, you bring up a good point about becoming "known" for something. The conversation, in this case, is really more about what on-site Disney restaurants are trying to accomplish. A restaurant charging these prices "in the real world" darn well better change it's menu regularly, or it will eventually die as it's regular patrons move, age or just stop coming in favor of something new. Within the walls of WDW, however, you can potentially make the case for consistency and reliability with the menu choices. Since most guests only eat there once, maybe twice a year at the most (if even that), it might be best to have a relatively stagnant menu so that people can comfortably expect to find "their favorites".
If I were the Chef, however, I wouldn't be long for staying somewhere that stifles my creativity.
JMO,
Brad