Here is why podcasting (as an authoring paradigm) never happened: audio is the same as video. Except not as good.
Video and audio are both time-based media. In fact, audio is simply a subset of video. You can see this on YouTube by finding a song you like, posted with lame photographs layered on top of it as the "video" part.
But it is actually much harder to edit audio than to edit video, because there is nothing to look at when you're editing (almost nothing -- you can get waveforms that help a little, but they're pretty hard to use effectively). Video has cues and transition points and also audio, so it's just easier to edit. Period.
So, audio is less good, less interesting, and harder to produce and edit than video, and it takes just as long to consume. Why would it ever become a popular consumer authoring medium? Exactly.
It's actually easier to understand the value of black-and-white TV after seeing color TV than it is to understand the value of audio-only on your computer, or iPod. Podcasting failed, and instead, iPods now all have tiny video screens!