I am not sure i see what is being done in groups as a new standalone UI for Buzz. There is a big difference between the way that a Buzz conversation thread works and an email/groups thread. Each item in groups stands alone as well as potentially being part of a thread, not the case in Buzz. There are similarities design wise with Buzz, but the same is true of Google Reader.
I do look forward to Buzz enhancements, but i am not sure the changes with groups are it.
Before Groups format was recently changed, there was a blog post from Google, which clearly indicated that Google is heading that direction of separating different functionality into different applications. I don't understand why we're still seeing a mess...