Update: Apple may be complying with an
FCC deadline of June 2, 2016 related to router software security rules gradually phased in since 2014, which would explain why the stock outage is limited to U.S. stores."Starting June 2, 2016, permissive changes will not be permitted for devices approved under the old rules, unless they meet the requirements of the new rules," the FCC writes. "All devices partially or completely approved under the old rules cannot be marketed starting June 2, 2016 unless they meet the requirements of the new rules in all the bands of operation."
(Thanks, Cole, Justin, and Corrode!)