I originally said that I was going to use a flash format and a torrent file as the media that would be made available to both watch/download the screencast material. I have never used a 3rd party swf viewer (aside from the flash player browser client). Eduardo Laranjeira kindly pointed me to the Swiff player from GlobFX. This is a free player that will allow you to play swf files that you have saved on your local machine, without the need for a browser based player.
This will give everyone the best of both worlds. The swf file will already be on the server available for people to watch on demand through the blog. There will also be an accompanying torrent file that people can use to download (and hopefully seed) the actual swf file to keep on their local machine.
Thanks to everyone who provided feedback and aided me in coming to this decision.