The maps being shown in the media (Flightradar etc) actually have nothing to do with radar.
They are dependent on a newer technology known as ADS-B, which is being touted as the replacement for traditional radar systems. At the moment, there are only a few sections of Australia where it's use is currently mandatory though the US and EU will be enforcing it by the latter end of this decade. Newer aircraft will come with this technology already installed, hence why you'll see a lot of aircraft on maps however there are still airlines flying around the world who won't have installed it in some of their older aircraft.
