The other day I posted some sarcastic comments on RSS. So to put the record straight, here is the real dope. RSS creates the appearance of push on the internet. Push is the idea that new things are pushed out to you automatically. Well not everything is pushed out to you. You subscribe to a "feed" and whenever anything new comes along on that feed, you automatically get it.
For example, I subscribe to a number of podcasts in iTunes. Every time I start iTunes, it goes out and looks for new versions of these podcasts and downloads them. Then I have to fiddle faddle around to get only the latest podcasts, the ones that I have not yet heard loaded onto my iPod. Most RSS readers are less intrusive than iTunes and appear to be more automatic. Then again, most RSS readers only deal with web pages that are quick to download compared to a podcast.
The reason you 'need' a RSS reader is that the internet is pull, not push. Your browser, RSS reader or whatever goes out and pulls back pages for you to read. An RSS reader works by periodically reading a feed page to see if anything has changed. Thus it creates the appearance of push on top of pull technology. At the other end, the most important thing about a RSS feed page is the convention about how it is updated. Unfortunately you can search far and wide and not find anything useful about this convention on how to run a feed.