No, it's not. What little we've had about super-secret legal requests isn't that companies have to lie about them. It's that they can't acknowledge them at all.

So the answer they give when asked, and they do get asked, is "no comment."

If they were voluntarily part of PRISM, and legally required to keep that quiet, I'd expect them to say "no comment."

Doing the opposite make so little sense. It means they're having to flat-out lie to their users, something very hard to recover from.