You seem like you know what you're talking about. Why do you think the average live-blogger uses something like Twitter over a video app like Color? It'd take just as long to sit through a live-blogged session as it would to just watch an audience video of the same event.
I'm not sure your question makes sense. People following an event over Twitter can easily multi-task; they can just scan every few minutes or less frequently as desired. Following the same event with video requires lots more bandwidth (more awkward when mobile), attention, noise (or headphones), screen real estate, etc. Unless you're extremely interested in the event, watching live video is usually a big waste of time.
