The problem about that is that is hard to keep track of your mails if every mail isn't in your inbasket.
For exaple, I work with 200+ workspaces, 3 other people in my team and 5 e-mail accounts. We receive like 20 mails per day by account and I know which one I have read and worked on because of my inbasket. If every mail goes to the workspace of the conversation it will almost impossible to keep track of every e-mail, considering that all new mail is going to that workspace, even the ones from other users, with are seen like unread for me.
Well, that is just my opinion.
Daniel.