I'm pretty sure that the reason there's sound in space is for the benefit of the viewer. You know, to add excitement to the movie and all.
Now keeping Luke's last name as Skywalker with an "old wizard" called "Old Ben" Kenobi so close by when they're supposed to be hiding? Now that's pushing it. (I realize it wasn't originally quite like that until Empire and Jedi, but its an early example of Lucas' retconning without covering all his bases)