1) Because if someone wants to have rss feed of your blog in her site or her browser
2) This is the normal expected behavior of any blog
3) Standard social nets like G plus or your FB have this ( blog = notes in fb )
4) All social scripts or social components of standard php scripts like Wordpress blog or Drupal blog have this by default
The entire site or the entire ( or part ) activity of an user is NOT what many users want to get in their browser or favorit rss reader or as feed in another site : blog posts are usually of substance and it has been usabilty standard for many years to have rss of blog posts.
In fact that is what some plug ins here utilize to draw data from BUT oxwall blog itself do not have this.
Last but not the least when you visit
http://blog.oxwall.org/ you can see the active rss icon in your browser ( IE and prev versions of FF and Opera and Safari)