WTF 2011 was definitely a better match for Fed. Not only the scoreline, in WTF he only produced 8 UEs as opposed to 20+ in IW.'
Notice how Fed now constantly uses heave top spin towards Rafa's BH, sort of like looping it and kicking it off the court. However he hits it dead flat to Rafa's FH. It sort of matches Fed's playing style, i.e. flat inside-outs and heavy top-spin inside-ins. Rafa likes to push insane angles with the BH so he probably couldn't do that easily with the topspin. And plus it's harder for him to moonball when the ball's coming dead fast down to your FH.