This looks like a typical DNS cache poisoning attack[1], which takes advantage of insecure DNS caching servers. Users of those caching servers will be sent to the wrong IP, so it is a successful attack of sorts. But there isn't much the target website can do to prevent it.
What makes you tell it looks like DNS poisoning? It if were DNS poisoning, some resolvers would have been poisoned but not all, while, here, everybody saw the attacker's IP address. http://www.bortzmeyer.org/observations-wikileaks.html
You may be right - I was basing that information off statements that it was only some users seeing the attack. I wasn't aware of a historic data source that could show otherwise.
Your analysis looks pretty good but I disagree that DNSSEC would have stopped the attack, because many users don't use validating resolvers.