What is the significance of this? It's not like they all signed up with Adobe to backdoor them. ('Coz if they did, that would be an extremely stupid way to go about it.) Probably legitimate users.
I think the implication here is that people might have signed up with the same username and password as they use for other things (e.g., their work email).
Not likely - the higher up you go in government, the more stringent they are with passwords for government provided services such as email. The NSA is probably the highest up there with that.