Its very simple. Sound in a vacuum in ther movies helps immerse the viewer into the action. Wether it's reaLISTIC OR NOT IS IRRELEVANT. Oops! Sorry for caps.  I know that if I am in a plane and another one flys by I hear certains sounds in a certain way. When I am watching a sci-fi film, Even though I know there is no sound in the vacuum of space it helps get me into the action. Oh and not even to mention Fireballs.

Pete