Say, one gets new directional tyres that are warranted to 60k miles and have 11/32" of tread when new.
If one rotates them at 20k miles (if directional; otherwise, at 10k, 20k and 30k, if non-directional and using a cross rotation), and then finds out at 40k miles that all four have reached their end of life -- 2/32" of tread left (or, alternatively, some at 2/32", others at 3/32") -- would that generally be a warrantable condition, or could the less frequent tyre rotation as above really shorten the life of the tyres by so much?
I don't see how less frequent rotation should realistically shorten the life of a tyre set by so much -- the whole purpose of rotation is to make sure the tyres wear out evenly, so you run a better luck of having to replace all of them at once, having better handling overall.
Is the above line of thought considered wrong? If so, does the other side have any proof to back up their claim?
After all, each mile gets that many nm of tread from front and rear axles each (or, as pointed out in one of the answers, from each individual tyre, due to differential imperfections), what difference does the rotation make to the total nm of tread eaten out by each mile from the set overall?