I've been travelling for the last couple of months, hence my lack of posting here, and had a brilliant experience with Apple Pay and Amex.
You get a notification on your phone whenever your card is used, whether it's through Apple Pay or by the card itself.
I got a notification for some transactions I didn't recognise (about $3,000 of flights on a Spanish airline). I called Amex immediately, and they cancelled the card and went through the fraud questions. No problems at all.
However the best thing was that a new card number was issued within 30 minutes of me phoning Amex, and loaded onto Apple Pay automatically. Therefore even though the card I had couldn't be used any more and I wouldn't get the new one until my return to Aus (they would have couriered it overseas but I was moving around a bit so chose to wait), I could use Apple Pay straight away.
Curiously though I'd say Apple Pay is more widely accepted in Australia than the US. Perhaps it's just where I shopped, but lots of places in the US didn't have the Tap/Paywave reader thing, and some that did have it still didn't take Apple Pay.
Anyway, I was slightly skeptical about using my phone to pay for things, as seen on an earlier post on this thread, but I'm now 110% of a convert!