You are absolutely correct.
The dozen or so hackers in this thread that expect that "security vulnerability" is some magic keyword that gets you talking to the head technical honcho of the security group have probably never answered phone calls for a big company. Phone support for somebody like AmEx is a huge burden of cost and manpower; the structure of the tree has been set firmly in place since the 1980's to take care of the most common 90% of issues using the least-paid person available. I'm sorry, if you're in the long tail you will just have to expect to wait extra. That goes double if you are not a cardmember (read: paying customer).
I am surprised that the above person in Australia got through at all, and that the CSR had latitude to try to spend time replicating the issue. In my opinion, for a credit card company, 20 minutes and a positive conclusion for a matter as rare as reporting a webapp vulnerability is a success.
Sure, none of you should be thrilled about the situation because as technically-oriented people with generous motives the system is not set up to serve you. But that's not a failure of the system, except maybe from your own individual perspective. Believe me, AmEx has done the cost-benefit analysis and they are saving boatloads of money by having those rare well-intentioned hackers listen to some hold music, because it is too expensive to sort you out from the thousands of loonies that got a phishing email. Security breaches are an acknowledged risk and they are already prepared to absorb their effects on multiple levels.