Turns out it was a right front upright failure, which then immediately overstressed the other side, so off they went.
The tethers attach the wheel hub to the suspension; if the entire front end falls off they do no good.
Virtually unheard of...
Several cars seem to look a little stressed just before turn 1: max braking at high speed, then they hit that bump.
Lotus and Virgin lost bits there too.
The TV cameraman was a little lucky - the wheel hit the camera while he was focusing on the car, and went over his head.