1. Beta testing does not find all problems, so it is possible for this to happen even if the page is beta tested.
I've always said that my best beta testers come out to play when I send "trouble free" code live. However, this isn't a small issue that should easily fall through the cracks. Combine this with the issue they had a month or so ago where online AH users couldn't type numbers into the AH fields, and it points more to shoddy testing than it does to something slipping through the cracks.
2. Issue is not happening to all players. Random problems are harder to troubleshoot. It can also mean that it's not happening to the ones trying to correct the problem, so it's harder to tell if they got it fixed.
How do you know it is not happening to all players? I have yet to see anyone post that it is working fine for them. It's true that lack of evidence does not prove something as true, but take a look at the tech support forums. Many of the threads about people having issues will also contain posts from people stating that they are not having the issue.
3. No obvious common features visable. It's happening to PCs and MACs. XP, Vista and Windows 7. IE, Firefox, Safari, Chrome, Opera.
Edit: forgot to add Opera to the list
That tells me it is not a browser issue and that the problem lives on the server side.
Regardless, it doesn't excuse the poor customer support. The only thing we've heard from Blizz on the matter is from a blue in a different forum who claims that the web people are aware of it. Things break, we get it, but keep your paying customers in the loop.