I can't hear you. I've got a banana in my spacesuit.
Sound comes to you in the form of vibrating air molecules. And what does outer space lack?
(Air is the answer I'm looking for, but "a really good café mocha" would also technically be accurate).
Yet, despite this fact, Sci Fi films constantly feature sound - roaring explosions, whining engines, "Pew Pew Pew"-ing lasers, the song of the spacewhale, and other silly things that make no sense.
If you'd rather know how it really works, see In Space No One Can Hear You Roll The Dice.
Game and Story Use
- Movies break the laws of physics because otherwise extended fight sequences in silence might be boring. In gaming, you're describing everything, anyway, so being realistic doesn't cost you viewers. The choice then becomes one of verisimilitude (and logic) vs familiarity (and a little bit of the Rule Of Cool).