There are a number of sites show the urls to various web pages but do not provide a link to the same. I'm sure you can think of a number of instances when this has happened to you. The last time, I came across this was just a few hours ago when I was testing the Auto Page feature on various blogs. Here's a screen shot. If you don't have Ziink Surfer or one of the other linkification addon, those green URLs you see, are just plain text. None of the links on this page actually point to those URLs.
Linkification is turned on by default and Ziink Surfer automatically linkifies any plain text URLs or email addresses. The appearance of the page is not changed though and the linkified text still look like plain text. This is to keep the new links from becoming a distraction.