We've discussed this before.
RvG brought it up :
vBulletin has always had a mod that does this: Reputation comment in post - karma for 3.5.
Here is an example of vBulletin 5 comments in posts.
I think a major benefit of comments on ("in") posts is that if people just want to comment on a small aspect of a post ... they can just add their 2 cents without junking up the thread with "Great Job", etc.
To me, comments in Posts will allow people to comment, without sprawling a thread over more and more pages.