Anthony,
From my understanding, all gem setting requires a mnimum depth of metal base to hold the stones. The various types of setting like grain, claw (prong), close (metal ring around stone) or channel, are such visible examples.
The invisible setting technique involves different sized stones tightly set on a metal base with almost no gaps. I think the different sizes is the key as each stone acts as the support for adjacent stones.
The full paved but calculated 'random-ness' of the stones is what gives Piaget snow-paved pieces that special look.
As they said: paved is not a technique but the look that is achieved with invisible setting. Other brands call it snow-setting.
Regards,
MTF