Here is the response I received:
"The main site feed is all the content that goes to the home page.
There are other feeds, like one for your blog, one for all screencasts, one for all media, etc… that would contain this post."
However, I notice that when you navigate to http://channel9.msdn.com/Media/Screencasts/ and click the "Subscribe" icon, you get redirected to the main site feed (http://channel9.msdn.com/Feeds/RSS/). I'm following up and will report back with how one is supposed to discover the "all screencasts" feed.
-Marc