Participating with government requests doesn't make these companies any money. It must be a major drag, actually. It involves lawyers, tech people, and trying to strike an uncomfortable balance between user trust and trying to persuade a court that a request should be denied.
This might be because they've been given a script, but it might also be because they chose to copy each other. They could copy each other out of not wanting to be "the odd one out." Any company that puts out a statement much different from the others risks being trusted less than the others. They could copy each other because they want people to jump to the conclusion that the government gave them a script (even if they didn't) so that people get more pissed than they already are.
As others have pointed out, the similarity could also be because the PR/lawyer response to this is so cookie cutter. I think the "not wanting to be the odd one out" would be the #1 mundane reason, though.
Google: "we have not joined any program that would give the U.S. government—or any other government—direct access to our servers"
FB: "Facebook is not and has never been part of any program to give the US or any other government direct access to our servers."
Google: "We had not heard of a program called PRISM until yesterday."
FB: "We hadn't even heard of PRISM before yesterday."
Google: "there needs to be a more transparent approach."
FB: "governments to be much more transparent about all programs"
Call me nutty, but this can't be coincidence.