Other have already nailed the main points driving adoption: simplified workflow and the desire to fill dead time (driving is mentioned in the article; for me it is cleaning the house.)
I don't think enough is made of the fantastic marketing channel that podcasting is. If you put out a high quality podcast you can get into the ear of your target market every week, and they are even going to seek you out. It's really hard to match this with another channel, IMHO. Blog posts are of course super competitive. There is just a deluge of content and playing the sharing game is hard work, and visitors bounce. Email newsletters perform well but there is no doubt that processing email is a chore for most. Video requires too much active engagement, and is too expensive to produce. Podcasts aren't so popular yet that the market is crowded, listeners hang around for a long time, and they seek out podcasts for fill time in their day, rather than your content having to compete with other tasks that demand more active attention.