It's not content producers that prefer Twitter, it's all the users that could never be bothered to setup an RSS reader (or Bloglines or whatever).
Twitter is a single point of consumption where with RSS you should be aware of the feeds to consume or have another site working on integrating RSS and staying up to date with the latests consumption points.
Because decentralized social systems don't grow very well, usually owing to lack of ease of use. Twitter, you sign up, plug in the name of some interesting people, and you're done.