2014 LEXUS IS 250 Wheels Problems

I EXPERIENCED UNUSUAL REAR TIRE WEAR. I TAKE MY LEXUS IN FOR SERVICE AT THE LEXUS DEALER EVERY 5000 MILES. I PURCHASED THE CAR AT 32,000 MILES. WHEN I WENT IN FOR MY 45,000 MILE SERVICE THIS WEEK, I WAS TOLD I NEEDED 2 NEW REAR TIRES. THEY WERE WORN EXCESSIVELY ON THE INSIDE TREAD AND THE INSIDE WALL HAD METAL THREADS SHOWING. YES I ALWAYS KEEP MY TIRES PROPERLY INFLATED. OF COURSE I PURCHASED NEW TIRES AND HAD AN ALIGNMENT DONE. I WAS TOLD BY THE LEXUS DEALER AND BY ANOTHER CAR REPAIR SHOP THAT THERE WAS NOTHING THAT I COULD DO TO PREVENT THE TIRES FROM WEARING OUT EVERY 15,000 MILES EVEN WITH A YEARLY ALIGNMENT. THEY BOTH TOLD ME THE FRONT AND REAR TIRES ARE DIFFERENT SIZES AND THEREFORE CANNOT BE ROTATED AND IT WAS SOMETHING ABOUT HOW LEXUS HAS THIS CAR SET UP, SOMETHING WITH THE...