While the forum is kind of quiet from a controversial thread point of view, I can see how you would think Newbies should be able to thank and such.
First of all, what typically happens with Newbies is that they start thanking every dang post they read--especially when they start a thread with a question. That's the MAIN reason. It rather defeats the purpose of the feature in the first place. Thanks are really for either especially useful or helpful posts--that is out of the ordinary--and in the Kitchen for showing public support on controversial topics.
Second, when a topic gets popular, if it's particularly heated, sometimes people who aren't fairing well in getting support for their positions get their friends to sign up on the forum to start adding their two cents. They would immediately start thanking their buddies and dissing everyone else--usually without having spent any time at all on the rest of the site or forum.
I prefer that people get a good feel for the forum all the way around before they start picking out things that they find especially useful or disagree with in our debate forum.