It is damn strange... You gain reputation power over a period of time and perhaps posts and depending on your group. IT's a very complicated system. I will have a good look at it when the right side of my brain wakes up and I stop drooling on my t-shirt.
"you aren't rating the user directly though. You are rating the user's post in a thread which then reflects on that user in the long run."
Plus "You can always change this behavior through changing the templates but they will lose track of their position in the thread."