Here are two factors that could play into the Hughes/GSP fight.
1. Pressure - Most of it is on George. Matt has nothing left to prove. If he loses to the heir apparent, it won't tarnish his rep. George, on the other hand, "needs" to win this fight or risk being put in the "close but no cigar" catagory. Edge - Hughes.
2. The Letdown - Matt is coming off the biggest, if not the best, fight of his career, defeating the legend. He might not be as motivated for a lesser known GSP. This fight is the biggest of GSP's career. Hard to see him lacking motivation. Edge - GSP
I'm admittedly partial, but I still think George will knock Matt out.