In light of all the attention on Facebook’s announcement this week that it has 500 million users, Randall Stross reminds us that no single website is as open, or important, as the Internet itself.

Every link found on the open Web, inviting a user to click and go somewhere else, is in essence a recommendation from the person who authored the page, posted it or broadcast it in a Tweet. It says, “I’ve taken the trouble to insert this link because I believe it will be worth your while to take a look.”

These recommendations are visible to search engines, which do far more than just tally how many recommendations point to this or that item. The engines trace backward to who linked to the recommender, then who linked to the recommender of the recommender, and so on. It’s a lot of computation to derive educated guesses about which recommendations are likely to lead to the best-informed sources of information and then placed at the top of a search results page.

No “friending” is needed to gain access; no company is in sole possession of the interconnections.

On the other side of a highly-complex wall is Facebook. The company wants that wall to work to its own benefit: your activity on the Web can be tracked and fed into the closed community, but none (or precious little) of what happens inside the community will be shared with the open web.

[Susan Herring, professor of information science at Indiana University], points to the recent introduction of the Facebook “Like” button at Web sites, which allows Facebook to note recommendations of those sites among one’s friends. The record of who clicks that “Like” button, however, is not part of the open Web; it’s Facebook’s. The public visibility of users’ Likes on Facebook depends on their privacy settings.

What makes Facebook’s privacy settings so complex is that it wants you (and your “friends”) to share enough information to make it worthwhile for companies to target you with advertisements, but it doesn’t want your information to appear outside its walls where non-members can see and link to it without logging in to Facebook. The only use Facebook has for search engines is to make sure they have just enough data to ensure that when someone searches for you, they see a link to your Facebook profile.