The Lexus IS cars (2006 and up) are known for inside tire edge wear, it is caused by the Ackerman angle in the front suspension. When making sharp turns in parking lots the front tires scuff the pavement and the result is rapid wear on the inside edge.
The wear varies from driver to driver on these cars, some people get 50,000 miles out of a set of tires, others chew though the front tires in 20,000 miles, all depends on the type of use. Most Lexus cars have 0.5 to 0.75 negative camber, that is not what is causing accelerated wear on the front tires.
I have seen tires worn down to the belts on the inside edge and still have 6/32" of tread in each tire grove.
