I've found that credit cards can have a varying exchange rate, so even though you purchase at the time of say 96AU to 100US (Talking cents here to keep it simple), the actual time of the money transfer can be different, so if the dollar drops a lot to say 80au/100us, then that's the amount you will pay, despite you actually making the purchase at the higher rate.

Then on top of that you may have to pay the old international transaction charge of some % as well. I found my CC to be worse than paypal at times. But then even using paypal, I'd still pay the international transaction amount.

It all depends on your CC as some have an option of no charge for the int. transaction, but of course the interest/yearly fee will be higher I guess.