It was an architecture change I think. I didn't do coding for quake 2, but if I remember correctly all sounds in Quake 2 were "sent in to the world." That means every time you shot, the server would send a packet detailing the fact that a sound (your bullet sound) needed to be played to all players around you. It also sent information relating to your actual "shot" itself. 2 separate things... your shot, and the sound.
In quake 3 its consolidated. Your client knows what sounds are associated with what weapons... so when someone fires, the server only sends the information for the shot itself (weapon, firing player, and a vector showing direction and speed.) The client plays the sound as soon as it receives the firing information so the server doesn't have to play the sound in to the world. In the case of other players, its delayed by your ping. In your own case, its instant. Your client already knows you shot your weapon.
That help any? The change was to make the game more network optimized.
Static