Why are Metal Cookers Hoods no longer need to be earthed?

Why are Metal Cookers Hoods no longer earthed these days IE they seem to be double insulated and don't require any earth but I would still be dubious that a live wire could come astray and touch the metal hood. Just bought a new one and it says 'must not be earthed' but I am in the old school of if there is metal that can be touched by the human hand that it should be earthed. I thought it was just this make of cooker hood but it seems other hoods from other manufacturers don't require earth these days either.