The New York Times reported (relatively) good second-quarter numbers today—especially in digital ads, up 20 percent in its division—and Jeff Bercovici says that should give the paper pause about its plans to implement a paywall next year.

Yet, in moving ahead with its plan to begin charging readers for website access in 2011, Robinson and the rest of the Times Co.’s management are behaving as though the digital ad picture weren’t bright and getting brighter. As Robinson noted on the earnings call, nytimes.com is the most popular U.S. newspaper website. Surely it risks losing at least some of its audience once its metered pay plan is in place, if not the 67% to 90% reduction suffered by the Times of London after it erected a rigid pay wall. Even assuming the Times is able to charge its advertisers more to reach its paying readers, the math may still not work out in its favor.

But if the math worked for a pay/free hybrid a few months ago—and that’s an open question with any business model in this industry these days—it still does. Probably.

As Bercovici notes, The New York Times isn’t making the mistake that Murdoch is making with the Times of London, which he’s putting completely behind a wall you can’t breach without forking over good money.

The NYT is going for a more Financial Times/Wall Street Journal approach that will allow it to extract subscription money from core readers (5 to 10 percent of visitors) while keeping individual stories free for the less-valuable-but-not-nothing one-off traffic from Google, Digg, Facebook, and the like. You’ll be able to flit on to the site from a friend’s email or from a search engine, read your story, click another one and be gone. If you want to read it every day from the home page, you’ll have to pony up for a subscription.

While it’s certainly good news to see the Times’s online ads up by a fifth from a year ago, especially since they were actually falling last year, that’s still coming off a very small base. Digital ads in the quarter brought in just over $50 million for the Times, The Boston Globe and the company’s other newspapers. That’s just 9 percent of the News Media Group’s revenues of $556 million.

It would take five and a half years of 20 percent annual growth in online ads—which seems unlikely—for digital advertising to reach 25 percent of division revenues—assuming print revenues stayed the same, which is not a good assumption.

But there’s a variable I haven’t accounted for yet, and that’s the iPad and its future ilk. The thing has taken off more quickly than anyone really imagined and I think it’s fair to say that it’s obviously a superior advertising medium than the Web is. E-reader revenue could provide a turbo boost to the digital-ads category over the next few quarters, and that could seriously alter the calculus.

I still think it’s likely that the Times will have to try to squeeze some bucks out of its heaviest readers online, but Bercovici is right that this is worth watching closely.

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Ryan Chittum is a former Wall Street Journal reporter, and deputy editor of The Audit, CJR's business section. If you see notable business journalism, give him a heads-up at rc2538@columbia.edu. Follow him on Twitter at @ryanchittum.