Facebook introduced the Subscribe button for web sites

The battle between Twitter and Facebook progresses so that the two networks have started to copy functionality.. Twitter unveiled a new design with profiles of brands, becoming more and more like Facebook, while the other social network first introduced Ticker for tracking activities like Twitter feed, and the button then Subscribe to monitor profiles like Twitter. The Subscribe button is now available for web sites, just like Twitter Follow.

Subscribe button for website work on the same way as the button for monitoring profiles on Facebook . When you click Subscribe on the account, the user starts to follow that account, and subscribe to public posts of the profiles that are displayed on the user's wall.
Subscribe to Web sites differ in that they are used on external web sites. When users click on the button they will automatically subscribe to news from the writer. With this Facebook gives higher popularity to journalists, bloggers and other people with web site to generate a larger base of subscribers, which gives greater effect on viral sharing. It seems that there is a rule with a subscription to only see posts that are marked as public at the social network.