How does someone wear out a set of tires in 12,600 miles and not notice anything unusual during routine mainenance. That sounds like someone who is not checking tire pressures, not rotating their tires, or just ignoring all the symptoms until the problem has gone on way too long.
Had the problem been noticed much earlier, Ford would have probably replaced the tires under warranty and even fixed whatever was causing the rapid wear. However, if the wear was due to improper inflation pressures, not rotating the tires, or just plain abuse, then that would not be their problem.
Since Michelin is taking care of 80% of the cost of replacements, perhaps the tires were defective, but it is very odd that all 4 tires were defective, and they were all mounted on one vehicle??? Then again, Michelin is still probably making money on the new tires even with a 80% discount by simply using an inflated price....That's why most tire warranties are not worth the paper they are written on.
...Rich