Yep, I have this...I sort of suspected when I read their terms and conditions that, since they aware more miles for the use of AmEx, fewer places take it. I try not to use my cards at all, but it's nice to know, for Airmiles purposes, if I do use them I at least can use the MasterCard if AmEx isn't accepted.
I seem to remember that Clark's takes American Express as well...hopefully, with everything you've read so far, Mungo, you should have a great start at building up that credit rating.