This isn't to say that you shouldn't give directly to support your favorite public radio shows and/or your local public radio station, naturally.
If that's all, it seems like a small price for drastically reduced hosting costs. And if there isn't already, there should be a protocol for "distribute via BitTorrent but ping the original seeder to let them know".
First you have to create the possibility for the people to download your podcast as a torrent. This sounds easy but is additional work. A new project that wants to tackle this is http://bitlove.org/ where podcasters just have to add their regular feed and the site will create a bittorrent feed and seed the torrents (extensive German descrpition: http://metaebene.me/2012/05/06/bitlove/)
The other problem is that users need to be able to easily download the torrent feeds. Some bittorrent clients support feeds, but right now only one podcast client understands bittorrent: http://http://www.getmiro.com/
I can't seem to find the exact message they sent me, but I believe the issue is that their licensing of content (mostly the music) on the show has specific rules about how that content is distributed (or not distributed).