In reply to Intrigued.

You have it spot on; many small, low-margin, or non-luxury merchants don't accept Amex because it's discount fee is ~1% greater than MasterCard/Visa; and, as you say, if the merchant won't accept it you simply pull out the MasterCard or Visa; the Apple fanboys whose card issuing bank has not come to terms with Apple, will have the same option, oh dear, to not be able to wave about your new iPhone—the end of time is nigh ...