I guess what you are asking is for all posts and all replies to be displayed in a tree-list format on the TOPIC page.
UBB.threads forum software is the next logical progression to that, because some TOPICS can have several hundred replies. Displaying several hundred replies to the same topic on a page will flood every other topic of discussion in that category off from the display. A discussion of PB&J could easily reach 100 replies, with each commenter discussing the bread, the contents, the cutting, the serving, what they like to drink with it, when...etc.
So in this case, the TOPIC LIST only displays the main topic, with all of the sub topic conversation within that, in a THREADED TREE
Looking at the forum you linked to, I see that your forum requires each TOPIC REPLY to have a subject, and it does not automatically populate the current subject of that TOPIC THREAD in to the reply. So A user is forced to enter something. UBB.threads will automatically populate the subject input for the user, but they can change it if they want to.
This is all one single topic, with the user entering in their own subject for the reply, rather than using the main subject.
UBB.threads does do what you are asking, except it rolls up all of the replies in to a single MAIN TOPIC. All of these replies to that MAIN TOPIC can be read by clicking through.
The screenshot above is a cleaned up version of the threaded mode that is currently in UBB.threads v7. I've spent a good portion of this past week giving a slight face-lift to some of lesser-used, but very powerful features of UBB.threads. You can expect these visual overhauls in 7.7.4. Though, the features and their descriptions remain the mostly same as what is currently in 7.7.3.