Chris not @ Toyo now

After looking at the pictures that he provided, it seems that the warn grooves (or sipes) may have been caused by a bad mold during the production of the tires. If you notice the wear is even and no other blocks have any noticeable wear on them except for the normal diving and there is no cupping of the tread in this area. The wear is confined to these 2 or 4 blocks. This happens when the spikes or knives that are used in the mold break off or become damaged in the processing. This should not affect the tire's wear or handling. What you might do is try to locate the Michelin zone representative and see if they will replace the tires due to the "minor defect". But this should not cause any major uneven wear problems or handling problems.

https://forums.audiworld.com/a4gen2/msgs/257786.phtml

ex-quattro PETE

sounds like a reasonable explanation to me.