Front Suspension problems of the 2006 Lexus GS430

I have a 2006 Lexus GS 430 with 17500 miles. When rotating tires at 8000 miles I noticed unusual wear on the inside edge of the front tires. I had the dealership check the alignment. At 17000 miles the wear on the inside edge continued and was a serious safety risk. The wear is difficult to see as it is on the inside edge of the tire and only noticeable with the tire removed on wheel turned full left or right. The wear resembles a groove or channel wearing on the inside edge of the contact patch on the tire. Discount tire inspected the tires and concluded camber wear. This was reported to yokohama who replaced all four tires. Lexus refused to acknowledge any problem and stand firm with a position of normal wear. This is a serious risk as the wear in not easily seen and poses a risk of tire failure at high speed. I feel there might be a design flaw in the suspension, steering, or alignment.