
They are real, and we still pay licence fees to receive TV.
The detector vans pick up the IF, true. This tells them what channel you
are watching. The can also pick up the line time base freq, and frame rate
(Try it with a LW/MW radio near telly, it picks up a sharp hum)

From this they can even watch (poor quality though) what *you* have on the
screen, by picking up re radiating junk.