The flight tracker system is similar to what has been used on ships for many years. GPS receivers on ships transmit the position data, course & speed to an internal network. A satellite transceiver then monitors this GPS data and periodically sends data up to a geosynchronous satellite receiver. Shore based systems, like the ship's corporate office, can then see, at all times, the current position, course & speed, of a ship.
Aircraft tracking websites have a premium service where you can have access to the up to date positions even in the middle of the ocean, but you have to pay extra if you want it. Most people won't pay the extra so all they see most of the time is estimated positions. Then when an aircraft is closer to a land based radar site those positions are updated in more real time.
Everything is based upon your desire to pay a fee for the extra service. Of course the airlines will pay the fee but most other people will not.
The ADS-B system is a recent upgrade to aircraft avionics packages that will allow other aircraft, even in the middle of the ocean, to see the positions of other aircraft in their immediate area. This is quite handy when you want to avoid a collision. Ships have been using a similar system for a long time and other ships can be seen on your radar display and an alarm can be set off if the system is programmed to do so. It's all quite nice when you want to survive.