Podcasting is RSS. That means that 26% of Americans (I don't have worldwide stats handy) depend on RSS every month.
So, more Americans use RSS every month than use Twitter.
So, more Americans use RSS every month than use Twitter.
For podcasts you need one mp3, usually quite compressed. For video you usually need more than one source, adaptable stream quality and good seeking (because most people do not watch videos end to end but only view parts of it).
This is probably not insurmountable but I guess we need better tools for creators to abstract all of this.
A 'podcatcher' (ie whatever app downloads it) is downloading the 'enclosure' url (which can point to any type of media) of the latest RSS 'item'.
Yes! Check out the deck and video from Edison Research's "The Podcast Consumer 2018" at http://www.edisonresearch.com/podcast-consumer-2018/.