CNET and Gizmodo have been sharing content for the last couple months. I confirmed that a partnership exists, but requests for additional information from either party were not fruitful.

Frankly, the most intriguing aspect of this partnership is already in plain view: The sites are posting the same articles. Take a look at this Gizmodo story then click over to the CNET version. Headlines change and there are subtle formatting differences, but the body copy is essentially the same.

Why is this relevant? If you’ve spent any time in the SEO world, you’ve probably heard of the semi-mythical duplication rule. As far as I can tell, CNET and Gizmodo are in duplication’s gray area.

The duplication penalty, or lack thereof

The cautionary tale of duplication generally goes like this: Google wants its search results to give precedence to the most popular/legitimate/relevant pages, and it’s tough to pull that off if the same articles appear on different domains. So Google uses filters to push copycats to the margins. Some people call this the “duplicate penalty,” but that’s a misnomer. Google isn’t slapping hands.

Here’s how Google describes its policy on cross-site duplication:

If you syndicate your content on other sites, Google will always show the version we think is most appropriate for users in each given search, which may or may not be the version you’d prefer. However, it is helpful to ensure that each site on which your content is syndicated includes a link back to your original article. You can also ask those who use your syndicated material to use the noindex meta tag to prevent search engines from indexing their version of the content.

The noindex meta tag doesn’t appear in the source code of these sample stories from Gizmodo and CNET. However, CNET’s version does link back to Gizmodo’s original. Gizmodo returns the favor when it’s hosting CNET content. (Both show up in a Google search for one of the article’s sentences: Gizmodo’s version is No. 1, CNET’s No. 4.)

Since the noindex tag represents the outer limits of my search engine understanding, I dropped a line to Brent Payne, the Tribune Co.’s head of SEO, to get his take on this type of content share.

Payne said variation between two similar articles could help both pieces rank well in search engines. But achieving this variation requires each story to have its own inbound links, as well as feature different title tags, different headlines, and altered HTML and body text. CNET and Gizmodo customize titles and headlines. The body copy doesn’t really change.

Payne noted that Google supports a “canonical” feature that signals the original version of a story (or the version that’s supposed to get the most attention). The canonical tool doesn’t appear to be in use by CNET or Gizmodo.

Payne also brought up an interesting point about Google News, which doesn’t share its big brother’s hang-ups about duplicate content. He said a duplicate article that cites the original — something CNET and Gizmodo both do — could give the original “extra weight” in Google News.

Why are they sharing?

All of this inside-SEO stuff is interesting, but it doesn’t really answer the big question: What’s the upside to duplication?

I’ve got a couple guesses:

— Marketing: It used to be you’d visit a publisher’s site to see their latest content, but readers now discover material in a variety of ways — Twitter, Facebook, Digg, RSS, etc. One analytics firm estimates on-site engagement dropped 50 percent between 2007-2009. Smart publishers are already addressing this by pushing content beyond their own sites. Toward that end, Gawker Media (owner of Gizmodo) could be using the CNET partnership to “find the next million people.”

— Money (obviously): An influx of content can theoretically generate page views, unique visitors, and better user-session times. Good metrics lead to better ad rates and more revenue.

Again, these are just guesses. I’m sure we’ve got SEO and marketing wizards in the audience, so please post a comment if you see clearer explanations.