The One With Chandler's Dad - S7-E22
Continuity mistake: When Monica and Chandler are in Las Vegas watching the burlesque show, Chandler turns the light on the middle of the table off to "hide" from his Dad. When Monica calls out saying "Waiter. Waitress.", the light is suddenly back on and remains on for the rest of the scene. (00:15:50)
Chosen answer: Posters are usually designed long after the film has been made, and by the marketing department. Decisions about the outfit may have been based solely on what was considered best by the marketing department (for instance, to match the color of the lettering in the title.) Also, Julia Roberts' head has been super-imposed onto a model's body in the poster image (just as Richard Gere's hair has been darkened). These are all creative marketing decisions.