Twitter: the new RSS?

Is it just me, or is Twitter becoming the new RSS? I'm seeing a number of websites using it where it doesn't belong, essentially for RSS purposes - whenever there's an update on the site, they tweet. While that's kind of nice, I guess, because RSS never really caught on in the mainstream, you have to wonder if a centralized service like this is sustainable - after all, RSS is distributed. Also, I guess that points out some of the failings of RSS - namely that sites never promoted it as much as they could and it wasn't every made as easy as your general public would like.