I have been asked to reflect on this issue recently and to be fair, I was not and still am not a podcast aficionado. Perhaps it is my age and I am slower to adapt. I don't, for the record, like books on tape either. From a pedagogical standpoint, I am not sure I am a strong auditory learner. Some students may not be either.
But, I have now done two podcasts and listened to others in education and I can see the value. Some have visual capacity too. Is there use additive? Is it to increase depth? Is it to explore tangential material? Perhaps it is to enable the professor to be more human by having him or her answer questions that are more personal.
Look at 2 minute podcasts/videos that LinkedIn is doing with respect to their top voices. I like them (mine is coming in the interest of full disclosure). I get a sense of the Top Voices; they are insightful; they are personal.
Bottom line: ask this about education: who are the intended viewers of education podcasts and what information is sought to be shared? Perhaps if we know that, we can reflect better on the future of podcasts across the K-20 pipeline.
As alternatives, what about animations? Cartoons? Music? Participatory videos where viewers create the ending? Graphic books?