Think again "or ask any brake manufacturer". Cast iron does not warp. Yes, excess pad deposits can cause shudder/vibration, but when you see a rotor being machined it is metal being removed. However, this is NOT because the rotor has warped to an untrue state. Lateral run out is caused by uneven side to side wear of the friction surface. This is the inconsistent thickness you refer to. Warpage would cause the rotor to form into an (extremely subtle) zig zag shape, not vary thickness.
If heat/heating and cooling caused rotor warpage, every car on the planet would require extremely frequent rotor replacement. Especially after some not too uncommon circumstances - emergency braking, long descents, driving in rain, driving through a puddle.....
Race cars have been hearing iron rotors cherry red for many decades. They'd need rotor changes more often than tires. Do some research, this is old news, not some new crazy theory.
As for having rotors turned- If the old ones aren't excessively corroded, turning is a perfectly acceptable procedure. Sometimes, replacements are so cheap that it just makes more sense or is easier to replace them.
Some major brake parts manufacturers actually recommend having new rotors turned, on the cars hub, when new, to prevent future lateral runout.