There are things you can learn from an in-person demo that you just can't get online. Like, where does the demonstrator place her feet? Or, What is he doing with his right (invisible) hand? Or that they reposition they tool rest, sometimes by millimeters, all the time--way more often than we amateurs ever do. It's hard to describe, but once you're past the beginner stage of learning, there are many, many subtle things you notice in-person.
Odie and Tim, if you go watch someone else turn in person, you'd undoubtedly be thinking to yourself, "Well, I can do that better with my grind", or "You've got way too much vibration". Much of what an advanced turner would see would not be new and useful, but there are always little nuggets in every demo. A new way of taking off the nub on the bottom of the bowl, how to use a bottom of the bowl gouge for something entirely different, or maybe Odie, you'd have seen an angled headstock for the first time 20 years ago and thought "Shazaam! That's what I need."