This is certainly an idea with good and interesting implications (but my very first thought was also "Google will be punked" before I even got to that part of the story!). Preventing this kind of punking with algorithms will prove to be impossible. Google will then discover, to their dismay, that it's also very-hard to prevent using real humans, IMO, but to them that won't really be a bad thing unless they somehow lose money, which is doubtful. With regard to:

"...we'll assume Google has thought this through and has some sort of plan."

Allow me to speculate wildly, since that's what I do best: Part of Google's plan, and it's rather ingenious as in the long run it effectively negates what otherwise would seem like legitimate privacy qualms on the part of all news-media-victims, is to gather quite a bit more very sweet and very valuable information. You'll probably need something like a gmail account to reply to a news story at first, but as the inevitable punkings escalate, they'll be able to legitimately harvest much more information, "to prevent spoofing." 

From both an information gathering and a PR perspective, this is truly a work of genius we're witnessing today. I always knew those nice Google-dudes were scary-smart, and today constitutes proof!
JMR

Rally online with fans of Dr. Ron Paul.

My only concern is this: if the responses are limited to only those mentioned in the article, wouldn't that allow conartists like Al Gore to spin every article out there mentioning him?  I can just see it now, The Economist prints an article exposing the charlatan on his carbon credit profits he gets to cleverly word a controlled response to spin away any and all criticism with his slick double talk.  It seems to me, given Google's how shall we say, non centerist view, that this is a potential means to control the damaging information flow by spin.

The object of life is not to be on the side of the majority but to escape finding oneself in the ranks of the insane. Marcus Aurelius

 How on earth do you PROVE  to google that : It's you in whatever article? And if someone responds before you, how do you disprove that? 

GOOGLE  new DNA site of course.

Entitlement over infrastructure every SINGLE time.

This is most puzzling, because is Google going to print "I did not rape that woman.....Monica Lewinski" in stories which will come up now in mass about Bill Clinton when Hillary attempts her second 8 year election.

So Charlie Manson can now respond and torture the Tate family again with details.

Cindy Sheehan now can not only rant, but rant herself as editor of her own news stories.

Kayne West will add at every story, "Kayne West is not a psycho and George Bush hates black people".

How is Google going to know it is Barak Obama and not some ghost writer as Democrats always employ?

Will Val Plame be able to include pictures of her in trysts with Joe Wilson to prove she was a spy in Europe?

This is going to be a fiasco as decent people will not use it as they do not have time and twirps like TB Andy will lie or just put up more vixen pictures of his wife to gain sympathy.

I really want to see though the Chicoms answering news stories. "No we did not rape, plunder, murder and annex Tibet. Chicoms only liberated Tibet from self rule by mothering it, executing criminals who did not agree to Chicom authority, removed wealth which Tibetans were unwilling to share and simply started a sexual education program via the military".

Guess Google is just going to write like the New York Times.

*HIC IACET ARTORIVS REX QVONDAM REXQVE FVTVRVS