OK, I'm in Sydney and if you were here, I would have recommended an independant mechanic (he owned LS400 and SC430) to see about the rotors.
Anyway, sounds like Lexus changed your rotors already, so there's nothing you can do now.
Next time, tell Lexus to call you if any work outside of a handbook service is required. Then you can instruct them not to change the rotors and you can get an independant shop to check the rotors - just incase the dealership was trying to rip you off.
BTW, my other car is a 350Z. I read about another 350Z owner that was quoted $5,800 to replace all rotors and pads by his Nissan dealer after just 30,000km. After having the brakes checked by a speciallist brake shop, he was advised that just the front pads needed changing - total cost $250.