As I stated, it is totally unscientific, and probably flies in the face of conventional wisdom. It is just something we have observed at our shop in Louisiana. Our notoriously bad roads and hot weather may be large contributing factors too. If I was a rocket scientist, I'd work at NASA, not sell tires.
What I am talking about is tires that the tread is separating from. Usually they still have the air pressure still inside. Some have the whole tread peeled off but are still inflated. I see many Marathons, just like that. I don't think they are necessarily over or underinflated.
A seriously underinflated (not overinflated) tire will usually fail with a sidewall blowout, due to excessive heat. After the tires blows out, it can peel the tread too....but it's usually secondary to blowing out. I don't want to stray off overinflation yet.
MY professional opinion, based on my observations, is an overinflated tire is very hazardous. Besides the potential for tread separation, a overinflated tire does not hang to the road as it should. It is riding purely on the center of the tread, and not the whole footprint of the tire. This could lead to stability problems also.