[derefr]

If they did do it, why would there not be at least one blog somewhere, of someone noticing that some domain doesn't resolve against 8.8.8.8, but does resolve against some other DNS provider?

Of course, this question would be silly under a dictatorship; the answer would just be "records have been suppressed." But we don't live in a dictatorship. Anyone in the US can use any DNS provider they like, even ones from outside the US. And anyone outside the US can use our DNS providers. So why would there be no evidence?

Mind you, I'm not necessarily arguing that Google wouldn't do this, if they were demanded to do so via a National Security Letter. I'm just arguing that you shouldn't conflate "no evidence that they're not willing to" with "already have in the past."