Don't forget that wound G string vs today's solid G string on electric guitars...try it once, and you'll hear (hopefully) what all that hoopla is about.
Oh, yeah...play thru a Fender Champ - one knob (volume), 7 watts...or get real carried away and pluck thru a tweed Bassman (with caps and such at 10-15% variation from one to the next)
So many things - mostly the players, the arrangements, the professionalism, and the 'get it right, right now, or get gone' approach to the business...
Oh - yeah - one other thing...no internet to blur the lines between reality, fantasy, and utter bullshit