Aaaaah. Makes sense now!

Passive radiators =/= passive speakers. A passive radiator is a driver assembly with no voice coil or magnet (so basically just a cone of paper) that will vibrate in sympathy with the other one due to air pressure fluctuations inside the speaker cabinet. It's not doing a great deal towards the sound (the cynical part of my brain suggests it's a cheap way of improving the looks/desirability of the product without forking out for another pair of drivers or the uprated amps to power them), I thought this sort of thing had fallen out of favour a long time ago so it didn't enter my head at all!