It appears as though the earlier website update that made it appear as though Marquardt vs. Demian Maia was the new UFC 22 main event it appears that was just a mistake made during the UFC's update of their website. The actual main event will be a fight between Nate Marquardt and Rousimar Palhares.
Palhares has developed a large following in the hardcore fanbase for his violent submission game. Marquardt will need to use his wrestling to try to keep the fight on the feet where his striking should give him an advantage.
SB Nation will have more updates as the card continues to change.