Originally Posted by LTJG Iferal
And even then, it was hardly ever used. Remember Star Trek II? After Spock lowers the Reliant's shields, Sulu locks and fires the phasers from helm. Later on, Chekov mans the "weapons console" and does some shooting; however, in Star Trek III, Scotty does the shooting from the nav station (we know it's the same bridge, unless all the scorch marks and damage are like some kind of new decor).
I do like the little pop-out single-button "joystick" that Chekov uses to fire the torpedoes in ST II. It's hidden behind a little panel, so a torpedo can't be fired accidentally before it's needed - understandable, considering that it apparently takes like 5 minutes to load another one.
You have to remember in ST III, Scotty rerouted a lot of the controls for the ship to make it automated so only two people, Kirk and Bones, could hijack it. The only reason the others were there was because they cared about Spock as well.
As far as why other stations could fire weapons. I figure that while the bridge has a dedicated weapons console that could control all the ships weapons and shields various other stations could do the same in either an emergency or incase of battle damage.