Time managing editor Richard Stengel has responded to criticism over the magazine’s decision to award 26-year-old Facebook founder Mark Zuckerberg “Person of the Year” for 2010, even though he didn’t win the magazine’s online poll.

“I think there’s a kind of short-term-ism in people’s thinking,” Stengel said. “‘Person of the Year’ is something I look at as a choice for the ages, not just a choice for the last six weeks.”

Stengel spoke with Yahoo blog The Cutline about the online poll, which overwhelmingly choose WikiLeaks founder Julian Assange for to honour (Zuckerberg finished 10th).

Media critics surmised that Stengel opted for the safer option by going with Zuckerberg, since Assange is a hated figure to the U.S. Justice Department. Slate editor-in-chief Jason Weisberg called Time (via Twitter) “gutless” for not naming the controversial whistleblower over the young billionaire. (Assange was runner-up instead).

But Stengel’s opinion is that while Assange certainly “had a big year”, his actions in 2010 won’t have the same impact as Zuckerberg’s will. “I think Assange will be a footnote five years from now,” he told Cutline. “Assange might not even be on anybody’s radar six months from now. I’m not thinking about the moment, but when you look three, five years from now, does it make sense?”

Stengel adds “there is no Julian Assange without Bradley Manning,” aka the army private many believe to be the whistleblower who leaked hundreds of thousands of classified documents (Manning has not been officially charged, although he is stuck in solitary confinement without access to the media). J-Source‘s Dale Bass suggests he may be a better story to pursue than Assange.

Facebook, on the other hand, grew by 500 million users in 2010 —- now, about one tenth of the world’s population has a Facebook profile. The blockbuster success of The Social Network, a film loosely based on Zuckerberg’s life (albeit with many artistic licenses) also helped raise Zuckerberg’s profile.

Stengel’s first “Person of the Year” choice —- “You” in 2006 (“for seizing the reins of the global media, for founding and framing the new digital democracy, [and] for working for nothing and beating the pros at their own game”) —- also raised criticism, although Time‘s Lev Grossman writes that the Facebook cover is considered “a bookend to that cover.”

“I do think something is going on deep down in the human character that’s changing and evolving,” Stengel said. Is there a bigger story than that? I don’t think so.”