Simply put, Rafa is not suited to HardCourts.
(Except for US Open where his last 3 results have been SF, SF, W. Even in 2008 when he had that exhausting year, and 2009 when he had the stomach muscle problem, he still made SF and without dropping many sets. He looks unstoppable there now, NYC is his town for the next few years. Also he looked impressive at Indoor World Tour Finals, beat Djokovic, Murray and took the 2nd set from Federer. If he had a bit more energy in that Final he'd have won. So when you consider what he did at the US Open and World Tour Finals last year, well those 2 courts are extremely different hardcourts, yet he did great. And this year he lost the Miami Final in a 3rd set tie-breaker to Djok, and he's never won Miami. Good opportunity in Canada Masters and Cincy Masters this year to pick up big ranking points)