I think there was another factor crucial for the tipping point: Adam Curry's relentless "people work" behind the scenes. You need someone who relentlessly promotes and pushes people for this new form. For videoblogging, this is Jay Dedman (and some others, but mostly Jay). I have been reading a lot about the adoption of new technology (in the social studies field, check out Bijker), and it's always like that: you need to shape your users at the same time as shaping the technology. Remember the Moog synthesizer? It only became big because of the relentless selling (to musicians) by their main sales guy. Adoption of the refrigerator in the US? The phone? The stories are the same, there is always a lot of co-construction of users and technology. It's not just that the technology pieces fell in place, and that the stories/myths fell in place, it's also that some key people played a crucial role in co-constructing users and technology. That's why when Curry says "users and developers party together", it's so important.