Honestly I can see a Fed civil service HR office doing that to make people feel better about not making the interview cut. My own experience with civil service in DOD jobs is that they are too slow and confused to get 'Decline' letters out. I understand that other government HR offices besides the ones I dealt with do make a much better effort on this, though.
I have applied for probably twenty different positions over my career, and have only received a 'Decline' letter once, telling me I didn't make the 'Best qualified' [Interview stage, usually] list, and then a week after reporting in to a new job that did tap me, I got a letter from the same place asking me in for an interview - they had apparently started over and based on the same applications and job announcement I had come out in the top three or four instead of in the basement.