Raptorex

You’ve no doubt seen the news about the T-Rex ancestor found…
http://news.bbc.co.uk/2/hi/science/nature/8259902.stm
http://www.nytimes.com/2009/09/18/science/18dinosaur.html?_r=1&hp
http://scienceblogs.com/notrocketscience/2009/09/raptorex_tiny_king_of_thieves_shows_how_tyrannosaurus_body_p.php
http://www.npr.org/templates/story/story.php?storyId=112925703
Raptorex kriegsteini is 1/100th the size of T-Rex. Of course, given the size of T-rex, this means that Raptorex, at 9 feet tall, weighed about as much as an adult human!
Even stranger, this ancestor has the same “jaws on legs” body plan that T-Rex has: relatively useless arms, oversized skull and teeth. The fact that this body plan “scaled up” so massively suggests that it is indeed a recipe for Mesozoic carnivore success!
It also makes me think that this nonsense that “T-Rex was just a scavenger” is patent nonsense. I can’t possibly see the evolutionary advantage to scavengers scaling up like this, and if Raptorex was a carnivore, why did the larger descendants change over to being obligate scavengers?