This is a design issue. The final call for this comes down to David (the guy who designed the new (and old too actually) C9 skin. I will bring it up with him and see what he thinks.
Just to clarify, I am meaning in this list here, where I can read the posted thread and the replies. It says the time of post, and I think it's easy to add the user, although the user name is then displayed twice, below the avatar and in the reply header.
It's just hard to find the user name under the avatar, because it is centered under the avatar picture, not left aligned like the date/time of the post/reply.