Someone doesn't have to create something to have an impact on how it turns out. For example, let's say one of the writers came in to George with an idea. George doesn't like it at first, and says no. Gary Kurtz then tells him to wait, they discuss the idea, Kurtz explains how he sees it working, and convinces George that it's a good idea worth using. Now, if it wasn't for Kurtz [or anyone else who would 'stand up' to George] then that idea wouldn't be used, and the story would be different.
I'm not saying that this type of scenario ever happened with Star Wars or Empire, or that Gary Kurtz ever influenced the story, I'm just saying, someone can have a big influence on the creative process of a movie without necessarily doing any creating.