With PRISM, if the allegations were false, Facebook and Google would deny them, but if they were true, Facebook and Google would still deny them. So the denial carries no information in and of itself. Parsing the denial might bear some clues--for instance, all these companies use the same technicalities and talking points.
What are the similar talking points? They both do strongly deny knowledge or participation in PRISM, but that's not really a talking point.
And I don't think it's an either-or situation: either it's the truth and they deny, or it's false and they deny. There's a third option: it's true, and they remain silent.
Also, is it such a crazy idea that Facebook, Google, etc. would get together and come up with their own talking points? That was my first reaction on seeing the similar statements -- that they're acting with a common purpose and agenda, but one that's their own, not the governments.
Why would companies who aren't collaborating with the NSA suddenly start collaborating with each other to deny collaborating with the NSA? Wouldn't they issue their own denials in their own words?
I don't really understand your question. It seems like you're asking why several groups, under attack in the same way, might get together to defend themselves, but I'd have thought that self-evident so -- what are you saying?