That might have something to do with it.
Others have said that the coverstock never finishes curing (ie: it's constantly curing). That would sense from all the reports about balls cracking while sitting out in a perfectly climate controlled environment - most tend to stay at a very low humidity level.
I keep all my unused balls stored in boxes, and in the plastic bags. I occassionally go through and rotate them - usually when I'm rearranging stuff in the garage, looking for a new ball to drill, or to take pics and post them for sale. It isn't often, maybe once or twice a year, and some probably never get touched.
I've got about 10 balls in the house, and another 80+ in the garage. Garage is detached, non-insulated, and not climate controlled. Winter temps get down below 30, and summer temps get into the 90s. I've only had 2 balls crack in the garage and 1 crack in the house. Of those 3, 2 of had some form of plug work (1 in the house, 1 in the garage)....and were not stored in a plastic bag or the box - there were all either sitting in a box or on a ball cup.
If it makes any difference, the balls were: AMF Titan SE, Track Mutant, and Ebonite V2 Sweet (x-out) - no plug work.