The scalpers circumvented the whole CC-entry restriction by buying up pre-paid Visa/Amex gift cards, and then placing the ticket orders on them, and then just shipping the gift cards to their buyers. So the buyers go to the venue with the gift cards, and the usher at the gate scans it like a regular credit card, and they're in!
(Buying CC-entry tickets on gift cards is not supposed to be allowed, but it doesn't really get enforced.)
But anyway... The next time there's a CC-entry tour, be it U2 or any other artist, I will buy my tickets via the same method as the scalpers, on a gift card. So that way, if something legitimately comes up, I won't be truly stuck and can try to get my money back... Lesson learned!