The services a ship uses to transmit their webcam data and their AIS data (tracking data) are different. Most ships do not use Satellite AIS (S-AIS) data which is why they go "Out Of Range". The terrestrial based AIS system which is free to use (one of the reasons it is used by most ships), is line of site and will limit the tracking of a ship to 100 miles or less from a shore based AIS relay station. If you want to dig further into it wikipedia has a decent overview of this AIS system - http://en.wikipedia.org/wiki/Automatic_Identification_System .
So, it is not too unusual to be able to see a live webcam image from a ship even though we can not receive its' AIS data which we need in order to track it.