Maybe it's different in the UK, but I've never been denied with Platinum or Centurion. I even purchased a very expensive diamond in a jewelry shop and the auth went through immediately without a phone call. A fact that greatly suprised the shopkeeper.

And Amex doesn't know or care how much money I have. They only care that I pay my bill each month whether it's $5000 or $50000.

Even if Centurion gave me some problems (it doesn't) the benefits far outweigh any minor incoveniences.