The only sci-fi I've ever seen that has no sound in space has been Firefly (Serenity had muffled sound effects in space). A video game doesn't have to be 100% realistic. That's what makes it a video game.
Personally I think the sound effects are fine. Maybe we could do with a few unique ones for special weapons like Mortars and SNACs, but I've never had a problem with the way Missiles and stuff launch. Though their explosions do seem grossly underrated. Maybe if I had my sound up higher it'd sound better.