Why have technologists such as Jonathan Schwartz, Adam Bosworth, and Jon Udell moved from traditional platforms to the blogosphere? Why have visionaries such as Adam Curry and Dave Winer bootstrapped the blogosphere with the podosphere? For the same reason: to improve the signal to noise and create content unencumbered by dilution and hidden agendas. The agendas are still there, but they're in broad daylight.
It's not a binary choice between journalism and development, blogging and podcasting, or even marketing and communicating. The power of metadata is additive. My vanity PubSub feed caught a podcast citation with Thomas Edison and my name in the same sentence. Sure got my attention. Net result: Harold Gilchrist joined my iPodder sub list and has flooded my Mac with 6, nope 7 just in, podcasts on something called the PODcast Browser. Then Mary Hodder pointed at Harold and Dave Winer pointed at Mary. It's a metadata swarm, as Ray Ozzie would put it.
I still don't have time to listen to all of these podcasts, especially when Trade Secrets such as the one Adam, Dave, and I recorded last longer than a nuanced John Krry answer. But a combination of breadcrumbs metadata, explicit such as the blog annotations above, and implicit such as attention metadata derived from usage characteristics (who reads/listens to who, what, in what order and for how long--or not) provides a roadmap for traversing the 'spheres.