If you did keep track of all that, it would be a bigger load. I can see that.
The MT forum doesn't store any of that, just the karma count. Just like here now. But before it will increment the karma count on a user, it sends a PM to the recipient from the sender with that info, but none stored permanently in the database, except in that one PM. You may delete that from your inbox if you like.
edit: The "Give karma" there is a two step process. You click the link in the topic, and you get another page with a form (message box) and a "Give karma" submit button.
Like I said, it isn't like YouTube.