You're absolutely right that video blogging is not for everyone, and not for every startup. I also agree that HN would not work as a web cam comment site.
For the right startups and founders with a certain type of DNA video related content (with transcripts and time-coded key points) can be an excellent marketing tactic. Just look at Gary Vaynerchuk - his videos are far from polished, but they are entertaining, and get the job done.