Tread depth when new starts at 9/32. Most other tires start at 10-11/32. Explains the 50,000 mile warranty. Less tread to start with.
My current Cooper tires started with 9.5/32 tread depth. After 24,000 miles they are already down to 5/32s (on a 65,000 mile warranty). They are wearing evenly all the way around but much faster than expected. I usually put new tires on at 3/32s so these will probably only go another 10,000-15,000 miles before needing to be replaced.