Not many web apps beyond Google, Yahoo, MSFT, Facebook, MySpace have much of a shot going "mainstream."

Most YC companies (in fact, none at this moment) will not go mainstream, yet several have been successful. Even a startup with a lot of traffic, like Scribd, is not mainstream, but it doesn't seem to have negatively affected them.

and see the number of video comments

Vid comments are of lower information content and of higher bandwidth... so they are of higher cost when you consume them. Also, most people don't wanna fix their hair etc to be bothered with them. Seesmic should study why video phones flopped...

i'd say that is valid for the majority of comments on the web. The exception seems to be Hacker News. Obviously that has something to do with the people not the medium, although a text comment is edited a multiple times.

I remember myself when i would scroll through the page of comments and read only the first ones, then suddenly you go through the page and must read all of them.

In the same manner although there were all these video comments i only viewed some.

It's about becoming a habit I guess.

Of course it took 15 years for people to get used or have a reason to text commenting...In few hundred! years maybe people may be will have a reason to use video phones and video commenting.