Dear tedhl,
For me, the extra centurion benefits in hk compare to platinum is that we can get the hotel membership (i.e. Hilton HHonors Gold VIP menbership and Hyatt gold passport with Diamond Status. We can use Hilton HHonors Gold VIP Card to get the discount at Conrad International Hong Kong which is my favor hotel (It is sound good to me). Also we can redeem the reward point for the air ticket (we can choose our favor airline).
However, we pay more annual fee but get less benefit compare to US Centurion cardmember. Amex does not send us the Departure Magazine which is exclusive for Platinum and Centurion Cardmember. The Magazine provides useful information about travel the good place in the world. The information are given by Platinum and Centurion Cardmember. They provide the useful experience of their travelling. I received the magazine every twice month when I was Canadian Platinum Cardmember.
By the way, I don't like the design of the black card. It is easy to see the finger print on it. Also there is no the word "CENTURION" print in front of the card. Compareing to platinum Card. There is the Word "PLATINUM" on it. So, someone will know what the card is.