Not sure that article is really relevant to us here in England.
I know the value of my 981 has sunk like a stone in the years I've had it, the only reason I've not sold it is I can't face to realise the depreciation!
Panamera which was bought in the knowledge it would drop - there does, on the 911's, seem to be an artificial valuation which now appears driven by the dealer network due to PCP/Lease - if you look outside the network similar cars are 10 to 15k cheaper