Brightwurks, who develop Feed My Inbox, have just posted a blog article explaining the Real-Time Delivery of blogs, feeds and news to an email inbox. The article discusses polling and real-time protocols. They list the Twitter API as a real-time protocol although they do know it's not actually an example of a real-time protocol and explain this later in the post. I've just posted a comment clarifying that although the Twitter API is not a real-time protocol it does use a real-time technology that we are starting to see being used more and more to deliver data in real-time.
Here's my comment in full slightly edit to better suit a blog post.
Although not a real-time protocol these are examples of using a HTTP Streaming API to receive instant notifications. HTTP Streaming seems to be becoming the API technology of choice when the speed of notifications really matters and I think we are going to see a lot more APIs offer this. I wrote an article recently on Programmable Web that covers this topic a bit further and discusses HTTP Streaming verses PubSubHubbub.
So, I would suggest you update the real-time protocols section and state HTTP Streaming being another method for real-time data delivery (still not strictly a protocol), use the Twitter API as an example of an API using HTTP Streaming to deliver data in real-time and also update the docs links to point to dev.twitter.com.
Hope this information is useful.