I think you may have been lucky. They can also be a bit more lenient at quiet times I guess... Reading through the thread, they look at the CS number at the back of the card to determine where it was issued.

I'm a reasonably frequent traveler with Eurostar, with Carte Blanche, and it does get VERY crowded on a Friday evening in London. I've seen someone be turned away with an Amex Plat issued in the UK because it was too busy.