I enjoy listening to podcasts on my PC in my spare time, but often times they refer to something that is happening that is visual that I have to imagine… just like radio.
I get the connection between podcasts and radio, but is there a technical reason why they don’t provide streaming video with podcasts, or do they just not do that? Is it a disk space/bandwidth issue?
There are loads of video podcasts. Go to itunes and click on podcast. There are three tabs at the top: All/Audio/Video. Click on video and gorge yourself.
(1) Video files are much larger than audio-only files, and thus they’re more “expensive” to store and to download or stream (possibly even prohibitively slow for people with really bad connections).
(2) There’s probably less demand for video podcasts, since many people listen to podcasts while doing other things, like driving or working, that demand their visual attention.
(3) That the podcasters can “refer to something that is happening that is visual that I have to imagine” can be an advantage. It means that they can much easier pretend something’s happening (for comic or dramatic effect) without having to act it out or visually depict it.
(4) Some podcasters may consider being heard but not seen a virtue. It means they don’t have to worry about how they look, what they’re wearing, whether they’re having a bad hair day, whether they get caught picking their nose, etc. Maybe the same reason picture phones never really caught on the way science fiction showed us they would?
I recorded/produced a podcast for a couple of years, and the guy I did that with is now doing a Videocast (hosted on YouTube), I’m not directly involved with that but chat to him about it. Just to give some background to my opinion.
Even simply the logistics of filming versus audio recording make creating a podcast far easier to manage than a videocast. The podcast, you can just be sitting at a desk near the computer, or even have co-hosts in separate locations recording a joint show via Skype.
Similarly the editing process is far simpler for Audio than Video. You can easily achieve a very professional look/feel with a fairly gentle learning curve with freeware. (I used to use Audacity). And “retakes” are easy to cut and adjust.
Video is not only harder, particularly if you want a professional look with graphics etc. It’s also much more of resource hog of your computer. Additionally unless you have someone happy to play cameraman, you have to either be content with a very static composition of your video or spend a lot of time stopping and starting to change the shot regularly.
I think there’s this website that actually does this, among about a hundred billion cat videos. 
No, seriously. There are dozens of streaming vlogs on Youtube. Is this not specifically what you’re thinking? Because the only difference I can see is that you’re not downloading it to view later. And as far as I’m concerned, that’s a limitation of podcasting, not a feature.
The difference is they won’t automatically be downloaded for you.
Also, a vlog often is just one person, and is inherently unscripted. Podcasts most often have multiple people and can very well be scripted.
For me, listening to podcasts and watching videos are two different things. I listen to podcasts while driving or doing chores, or otherwise engaged, but still able to listen to someone talk.
Watching videos is an entirely different kind of activity that demands way more attention. If one of the podcasts I regularly listen to went to video, I’d find someone else to listen to.
I come home, I plug my phone into my desktop, it charges and syncs automatically. Fresh podcasts are there whenever I want them. Life is good.