RSS is simply a notification of a change or new content on website. The notification can be sent by email. Even better is through feedreader. Google Reader, Bloglines, Attensa, and Newsgator are examples. (Most of you reading this are getting it through a feedreader. There are few getting it by email and some keep coming back to the page to read the content.)
RSS disaggregates the content from its source. You do not need to go back to the website to find the change or discover the new content. The content is pushed to the subscribers of the RSS feed for the website. Wikis publish the changes to a wiki page or the addition of another wiki page to the subscribers of the wiki. Blogs push out new blog post with RSS.
The power of RSS is to showing the flow of information rather than just seeing static content. RSS turns a webpage from a repository of information into a broadcaster of information.