Fed has achieved nothing of note at the USO in 4 years...I'm sure Mats and Goran factored that into the equation as well.
2009: final, lost in 5 sets was 2 points away from victory
2010: semis, had 2 MPs
2011: semis, had 2 MPs
Roger has reached the final 6 consecutive years and had MPs in the last 2 years to reach the finals.
I think only this makes him a favourite for the US Open.