A long time ago, circa 80s as Jason mentioned, it was a normal thing to turn drums and rotors. From a business standpoint, what Jason said also makes sense, if you turn a rotor and there's a problem, now its your problem. If you replace a rotor and it's a problem, you warranty it. That's all from a repair shop viewpoint and makes perfect sense. From a DIY owner's viewpoint, if a rotor is not too worn down and doesn't have any scores in it, there's no reason you can't just give it a quick sanding to break the glaze and leave it at that. I have done lots of pad replacements and don't touch the rotors at all. If money is no object and you want the VERY best from your brake job, replace pads rotors and hardware. If you are trying to do it economically, you can usually just replace the pads without doing much of anything else.
