Vivian: Oh...Look honey, I have a runner in my pantyhose. Oops! I'm not wearing panty hose!
Woman at elevator: Shut your mouth, dear.
Edward: What makes you think I am a lawyer?
Vivian: You have that sharp, useless look about you.
Edward: You can't charge me for directions.
Vivian: I can do anything I want, baby. I ain't lost.
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.