I can't claim to understand 4chan, but it reminds me of 4chan's past reactions to negative press such as the "Ya dun goofed" incident.
For those who didn't notice "Ya dun goofed" here is a brief summary: 4chan trolled a young girl to tears, provoking the rage of her dad, who then called the police. The incident of cyber bullying caused widespread media coverage, and 4chan responded by briefly adding music to /b/, removing porn ads, calling it SFW (with the blue background theme), posting kittens and rainbows, and deleting porn threads. Needless to say /b/ quickly tired of this and returned to their old ways. However, I mentioned it as an example of 4chan's long history of alternating between making themselves look really bad, and then trying to make themselves look good.
I may be that they are running this DDOS on themselves so that they will be seen as innocent victims just like Paypal, Mastercard, etc.
There are so many legal difficulties with DDoS, you can almost guarantee that neither a bank nor a government agency is likely to do it, regardless of paranoid delusions. As for the government, they generally have more effective means so long as their target's servers aren't located in the ass-end of nowhere.
You've been watching too many movies. In reality most spy and law enforcement agencies are huge, bureaucratic messes that can barely get anything done, even if national security is clearly at stake.
Can you imagine how many meetings it would take for the US security agencies to go about hiring a botnet? Whereas they have a pretty much unlimited supply of heavies on retainer.
Especially given the DDOS against Wikileaks, I'm pretty sure they also have at least one botnet on retainer.
And there have been voices high up in the government saying that the US needs to develop offensive cyberwarfare capability. If that's not a call to develop state-owned botnets... the people in charge don't understand technology.
Of course, the use of the term cyberwarfare might be a giveaway anyway.
In any case, I'm sure it's a pretty simple matter for some people in the CIA to quietly hire out a botnet.