I have been dealing with the same thing over the last few days and after repeated checks of my tires both via gauge and inspections, I think my treadwear has gone down just enough to warrant re-calibration
My pressure remains constant and it seems that when I have more weight in the rear, ie trunk and rear passengers, the TIRE DEFECT comes up.
I was in Tampa entertaining clients when it happened and I took it to Reeves Imports the next day and the Manager of their tire shop checked them out personally and gave them the OK. He said I had a little less than 50% on the rears and that I may have to recalibrate as my fronts still had about 70% and the difference in rotational speed was probably causing the message