Another observation about Firefly though: I think the "space-without-sound" stuff was only possible because it was a TV show without any space battles. And the first moment there was a space battle (in Serenity) they started to have sound in space again for dramatic reasons.
But they really didn't. They had music representing sounds (like the drums when Mal fires the gun at the Reaver ship). It was done for dramatic effect, yes, but it was a lot better than real "pew pew" laser sounds or explosions.