Via MMA Mania comes this quote from UFC president Dana White:
"The bout between Rashad Evans and Thiago Silva is a fight we always talked about as a main event, and now these guys have the chance to headline UFC 108 and kick off the new year in impressive fashion. At the same time, we wish Antonio Nogueira a speedy recovery and can't wait for his return."
Despite what Dana says this was never really a main event caliber fight. Both Evans and Silva are coming off fights where they got slept by Lyoto Machida which makes it hard to sell the fight as having a deep relevance to the division overall. Evans has never had to be the "name" in a main event and how much of a draw he is is very much in question.
Make no mistake, this is not a fight the promotion wanted as a main event. This is the direct result of all the injuries that have happened in the UFC over the past month.