2005 Other Hyundai Models FRONT ROTORS DIAMENTIONALLY UNSTAB

I BOUGHT MY HYUNDAI XG350L NEW FROM A DEALER IN 2005. THE BRAKES SHUDDERED SLIGHTLY WHEN I BOUGHT THE CAR BUT I THOUGHT THE NEEDED TO BE BURNISHED IN AND WOULD SMOOTH OUT. THE DEALER REPLACED THE FRONT ROTORS AND CALIPERS AT 50000 MILES. BRAKING WAS SMOOTH FOR A WHILE BUT THE VIBRATION LATER REAPPEAERD. AT ABOUT 18000 MILES LATER HYUNDAI TELLS ME THIS IS NORMAL WEAR AND TEAR, AND WILL CUT DOWN THE ROTORS TO ELIMINATE THE VIBRATION. I DRIVE ABOUT 7000 MI /YEAR AND DOWNSHIFT TO REDUCE VIBRATION. HAVE YOU HEARD OF THIS PROBLEM ? I DONT WANT TO DO A BRAKE JOB EVERY 5000 MILES. WHAT TO DO?