I don't think that guy paid attention to the video. Some of his points were addressed in the video, like people seeing what you're typing at the same time (which can be disabled if you want) (reason 2).
For reason 3, since Wave acts like a tree, you can actually talk behind people's backs without everyone else seeing your sub-conversation. Not to mention, you can spin off a Wave (branching for us version control folk) yet pick up changes to the original if you want to since it knows about it's parent. Then you can share the copied version with other people. If people will actually do that is another issue.
And for reason 1, the idea of editing the original (which is all version controlled so there is no data loss) is that you can have a concise thread of discussion rather than having to weed through many forwards and "hidden" added content in the replies.
Some of the demos, like the chess match I think are actually really cool. I tried explaining this to some non-technical friends of mine this weekend and they just didn't get as excited as me, so maybe I'm wrong in thinking this is going to be widely adopted. I'm seeing most people get hung up on the lack of perceived usefulness of the collaboration aspects of the technology.
I wonder if you can remove people from the Wave later (like if they haven't made contributions). I get the feeling it's sort of like a message board where the person who created the Wave is the owner and can actually destroy the Wave if they want to, as seen when the demo shows the guy finishing the Wave and then removing it from the other person's screen repeatedly. Either way, I'm sure it's going to fun to play with. Something tells me now though that it might take a while for non-tech people to adopt, but I'm guessing tech people (especially intranet type stuff) will grow quickly.
