Every single house has much more rooms than only the cellar, yet everything is built on that. I did not say TUS is a simple SMF site with a few extras, I said that basically it's built onto it. If you remember the time when this website was launched, it was only a forum actually, there was practically nothing else.
And as far as users go, on this site especially, most of them care about the features on the site, which is the backend.