I received some additional information on the Nikon free maintenance service initiative: the emails were sent to about 4,300 D800/D800E owners, as well as to aprox. 100 D700 owners and around 100 D7100 owners. Unfortunately, if you did not receive an email, you will not be eligible for this offer. This service will not be offered to everyone. To make sure you don't miss on any similar offers in the future, make sure your camera is registered with Nikon.
Update: for now the Nikon free maintenance service initiative is available only in the US: