This isn't exactly true. They are listing "new" Apple-branded silicone and leather cases that are compatible with the iP8 and iP7. These cases are listed as "new" and are not available for store pickup anywhere until 9/18.
My guess is that they tweaked the case slightly to accommodate the *slightly* larger iP8 (look up the dimensions and compare the iP8 to the iP7) and that this new case is backward-compatible with the iP7.
That said, they may not have changed a single thing with the case, but they are definitely marketing it as a "new" case.