Snowden says nothing about backdoor'ed Windows.

And _NSAKEY... There is no evidence that it was ever part of a backdoor. But it is good for a laugh.

It's safe to assume that Windows is backdoored, as it's closed, not audiatable and is a part of PRISM. It's not a proof, but this is how good opsec works.

And yes, this is not equivalent to what the parent said, but your reaction should be similar.