I don't know about individuals' podcasts, but real radiostations are doing it too. It's the easiest way I know of to get time- and space-shifted radio shows.
I totally agree. I can listen to the Democracy Now! Podcast
anytime I want. On the subway, in the car, whenever. That means I can catch up on the events of the day during otherwise wasted time. This is huge for me. I repeat: otherwise wasted time affords me the opportunity to become a more informed citizen.
Also, I visit a bunch of different new sites every day, and I find that the radio format is a much better way for me personally to take in information. I'm sure this is the same with many other people (but not all, of course). I get more out of listening to one Democracy Now!
broadcast then I do reading a whole slew of print articles.
And just because most self-produced stuff is crap, doesn't mean it will all be. Someone will come up with a smart way to filter the crap out. Someone always does.
Furthermore, the arena is not just open to radio. Any kind of recorded audio--old lectures are also available. Say your favorite mathematician gave a famous lecture in 1986. Guess what? You can listen to it on the subway. Pretty damn cool if you ask me.