While I find the abusive techniques being reported as abhorrent as the next fellow, I would challenge the assertion that it's their job to disclose security issues.
I'm not saying that they morally are not obligated. They are morally obligated to do so, in my personal opinion, to maintain the general fabric of security for the country.
But I'm not so sure that they have a legal obligation to do so.
There are some pretty convincing cases where they could argue that an obscure exploit can be disclosed and upgrade the digital security of the nation by 0.01% or they could hold onto it and use it to help prevent specific bad actors with big plans.
So yes, while I'd like to think we're all above board and working towards a bright shiny future with full disclosure, I'm not sure that the charter for agencies running covert ops lists vulnerability disclosure as their operational mandate.