[mywittyname]

There's a symbiotic relationship that exists with podcasting that doesn't necessary exist for other media. Podcasters want to reach the largest possible audience because they are paid relative to viewership. Hosting their own content has an expense and doesn't provide them with very effective discoverability. Podcast platforms make their money from having a large collection of podcasts and, for spotify/itunes, podcasts don't generally have royalty fees associated with playback.

This isn't really possible with things like movies.

[Pxtl]

Yes, but none of that has anything to do with why RSS+mp3 won. If somebody invented podcasts today it would be a walled garden, not an open format where I can point any podcatcher at any host and get the feed.