whats all this crap about not machineing skyline rotors, thats the biggest load of crap ive ever heard, you should be machining your discs whenever you replace pads so they bed in properly, and they get warped by things like getting them hot then having to sit at traffic lights with your foot on the break, thats why when you finish your ;aps at the track you dont put your handbreak on you just let the car sit there so they can cool down with no uneven pressure, yes they are floating, not need for torque specs. and after time your rotors will get glazed, thats one reason for squeal and another reason to machine them when you get new pads, when they wear they dont wear flat they will get grooves in them, if you just scratch them up a bit you wont make them flat, then when you put your new pads in they wont be contacting the whole surface and will wear unevenly.
also your disc will warp easier the thinner they are.