Why do publishers of websites feel that they also need to have their own blog?

I can understand a newsletter, but why also a blog? And why would they also want to have RSS feeds or podcasts.

I've never used them so maybe I don't fully understand their function, but at first impression it seems a lot of duplication to me

Could you explain what each of these media is supposed to do and how each one differs from the others?

Thanks.



Websites, newsletters, blogs