Jon reports that the results are surprisingly accurate, but he edits them to make people read better than they sound and to make them more readable. This process takes an hour or so per episode--almost one-to-one on a time scale. Of course Jon's also spent time editing the audio for the podcast as well. That's a considerable time investment, but the results show quality.
Why do this? One answer is that Google indexes written text, not audio, so getting search placement requires text. Another reason is that some people simply prefer to read instead of listen.
Doug Kaye used to create transcripts of IT Conversations shows back when it was mostly interviews he was doing. He stopped, mostly because of the cost, I think. We create fairly extensive landing pages for shows that should contain significant textual content to help Google index the shows correctly. Still, there's no way you can completely capture the multiple twists and turns of a standard show in a page of text.