PRISM and the related Verizon records requests seems to have been authorized following the FISA scandals of ’05-’06.
Which is interesting in the context of Obama’s recent nominee to be the next FBI director, who opposed the FISA warrentless wiretapping program, despite significant pressure from the Bush White House.
For further background, check out the National Security Letter framework set up by PATRIOT Act, declared unconstitutional, revised, declared unconstitutional as of the most recent judiciary review. For about 10 years, Nicholas Merrill and the ACLU fought to expose it, eventually winning the right of removal of the gag order that prevented Nick from doing so.
With this context, it’s quite possible that the oddly similar denials by Facebook, Google, and Apple, among others, are driven by specific requirements in whatever National Security Letters and accompanying gag orders were part of the information request.