So the whole thing about using Apple Pay to pay for your Apple Watch and then between the purchase and today the card gets removed from Apple Pay (mine happened when I updated my phone to iOS 8.4 beta 1) actually does break your purchase. I read here people saying that as long as the payment is already processing you should be fine, but when I just now checked my order status it said that the payment can not be verified.
Luckily it gave me the option to update my payment info right. It game me the option to retry the purchase with the prior method or enter a new payment option. To be safe I just went on and enter a new payment option via my credit card (which is the same one I had hooked up to Apple Pay).
Hopefully it doesn't get delayed.
Also I preordered the 42mm SS milanese loop watch so looks like they are charging for it.