Movies that have had the gun sounds/explosions replaced on DVD/Blu-ray

I've noticed that certain films on DVD/Blu-ray, particularly older ones like Scarface and The Terminator, have had the original gun sounds/explosions replaced with more modern-sounding gun sounds/explosions.  

Anybody know why this happens?  Is it something that is just part of the remastering as the picture quality gets remastered?

The video below will show you what I'm talking about.