see you auntie said:

So it's fairly well known to nerds in the know that Lucas' friends and colleagues Gloria Katz and Willard Huyck did an uncredited dialogue polish on the final draft of Star Wars prior to the film going into production.

Seems to me those two contributed quite a lot more to the script than is often mentioned. George just can't write dialogue as good as that attributed to Katz and Huyck (and probably there are many other examples in Star Wars not credited to them).