I replaced my Bridgestones at 7,250 miles and .3 tread. I was at the wear bars and headed to the track for the first time and did not want to fail inspection. I do not lay down rubber until the night before I change them out.
I long ago tried to use mileage warranty's only to have them tell me I drove too hard. Once I was even accused of spinning the front tires on my 280Z.
I just accept that tires that get lots of cornering wear are not covered. That's life.
My Michelins are better.