Hacking the NSA website is not hacking the NSA. Hacking a website is relatively easy and not that interesting to people who deal with servers day-to-day.
Well, more to the point, it doesn't imply anything about the business end of the agency's systems being compromised. If you hacked into the actual CIA or NSA as in having similar access to an authenticated agent, that would be quite bad for them. Taking down their website is something they don't really care about.
Right, see. When you say "Relatively easy" do you mean: "it is just subtly easier that compromising the NSA itself" or: "I'm surprised it doesn't happen every day"