Update: I found a possible answer on Apple's forums. The "why" is over-my-head. Shutting down my cable modem, Airport Express wireless router, and, for good measure, my extender and computer for ~12 hours fixed the issue.
Good to hear. Basically you were lucky that your WAN / public IP got re-assigned. Comcast's DHCP IP address's are sort of known as being *sticky* dynamic and are tied to the MAC address of the device that is connected directly to the LAN port of the cable modem which means that they can change but are typically re-assigned even after an extended period of time that the modem is off-line. Your old IP must have been needed somewhere else and got withdrawn back in to the IP pool. I've had the same WAN / public IP for more than two years even after having the modem un-plugged for a month on vacation.
FYI. You could have gotten an instant change of public IP address by cloning a different MAC address in to your router's MAC address cloning feature. Keep this in mind for the future. :-)
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