you are correct. there is no 250k requirement for icc centurion. in fact, there is no requirement to even hold an existing amex card.
my private bank submitted the application on my behalf. essentially, amex centurion told me that, as i had NO prior amex history, they would require a bank guarantee of X, which my private bank gladly provided.
really, if your private bank is putting up the guarantee, there really is no reason for them to decline your application.
the icc (dollar and euro) concierge/travel services are provided by amex uk directly and not outsourced like us centurion (circles). they aren't the most useful but they are very friendly and respond very promptly to emails (usually 25-30 minutes MAX response time).
-t.