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.
