How often are projects forked anyway? Here I am, viewing open source project XYZ, and the upper right of the page says "Fork Us" and tends to be the only link on the entire page that points to GitHub. Most people just want to view your GitHub project page, they don't actually care about forking your project. I think almost all cases of "Fork Us" could be re-marketed as "View our GitHub" or "Contribute to our project". I mean, would you rather have a developer fork your project and do their own thing, or contribute to your project?
I guess it's similar to people saying 'Like us on Facebook'
It's a direct call to action instead of 'please come & take a look'<p>It's also a metric that's instantly visible, contributes towards popularity, where as page views are not shared nor are they an indication of quality.
I've got a few very small projects on github. On several occasions, people have forked a project, made a change to it and sent a pull request, which I then merged. That seems to me to be precisely how github should work as a social coding site.