Why are eggs getting harder to peel?

http://www.wired.com/wiredscience/2009/10/eggs-hard-to-peel/

As an egg ages, it loses some carbon dioxide through tiny pores in the shell, making the egg white more basic. At the same time, it loses moisture, which increases the size of the “air cell” at the bottom of the shell, between the inner and outer membranes. The dynamics of this process are, in the words of a University of California, Davis agriculture publication, “not completely understood,” but the combination of these changes makes an old egg a lot easier to peel than a one that is fresh out of the bird.

...

“As the contents of the egg contracts and the air cell enlarges, the shell becomes easier to peel,” the USDA Shell Eggs from Farm to Table fact sheet states. “For this reason, older eggs make better candidates for hard cooking,”