None of my USA issued credit cards have PINs, and they've worked fine in several European countries. My debit cards have PINs, and I've had problems using them overseas, even when the banks were notified before the trip.

As for immediately deactivating a card, not everyone carries the phone numbers for their credit card issuers with them, and most card issuers seem to keep American business hours for live customer service. So to deactivate a card, first you'd have to get online to find a phone number, then make an international phone call, which might mean using a landline if you don't have the right travel sim, and then trying to convince customer service to cancel a card for which you can't give them the card number because most of us don't memorize 16 digit card numbers.