This was not an attack scenario. An attack scenario is one where a person or group of people is attacking the Bitcoin network. This was a bug, and one that would have been very difficult to discover without running a network on the scale and complexity of the real network, meaning one that would have been extremely difficult to discover ahead of time by an adversary and exploited by her.
Insofar as this or future versions of Bitcoin might still have critical bugs that require social consensus to fix, then yes, Bitcoin is not guaranteed to be totally independent of the type of ad hoc centralized governing structure that emerges in IRC channels and Skype chats. But a bug is a failure of implementation, not the concept. Bitcoin, the concept, is sound, and is a major breakthrough that is not appreciated by OP's analysis.
Insofar as this or future versions of Bitcoin might still have critical bugs that require social consensus to fix, then yes, Bitcoin is not guaranteed to be totally independent of the type of ad hoc centralized governing structure that emerges in IRC channels and Skype chats. But a bug is a failure of implementation, not the concept. Bitcoin, the concept, is sound, and is a major breakthrough that is not appreciated by OP's analysis.