Geeks and early adopters are the only people who Google could expect to stick with it in it's current state (or to at least try it again later).
In any case, it seems clear that Google Wave is still in heavy development. More than any other Google app, Wave deserves and needs its 'preview' appelation. The early adopters are the ones who are going to provide feedback. And even if most people are wrong in comparing Wave to Twitter (I'll be honest, I have not seen that comparison made once, but I don't read Scoble either), it's true that the Wave interface is not the most graceful or immediately-obvious thing to ever roll out of the Google garage.
Something which can let you do a small, but consistent and very useful set of operations everywhere will eventually attract the largest body of users. This is what Google should be aiming for with the Chrome OS. They should make sure that the Wave protocol is throughout that product, and everything else that they do. If they can eliminate the dozens or hundreds of minor frustrations faced daily by users due to the imperfect seamlessness of the current OS/browser/apps toolset, Google will garner tons of mainstream love.
Perhaps Google needs to try seeding entire companies at once -- preferably not companies composed entirely of geeks who know what Etherpad is -- instead of handing out invites to random folks. On the other hand, such a strategy would limit their growth rate and constrain their feedback in a different way. It's tricky.
I think Google Wave is great. But it is by its nature revolutionary, maybe we need more time to redefine how we think of "communication on the Internet"
You can't test a collaboration tool if the people you collaborate with can't frigging access it.
One could argue that social media types are more concerned with public communication than private collaboration.