This is silly. He WON in 2010 and you are using that as an example? He made the finals in 2011 and lost to Novak, just like he did I think 7 times in a row in finals on all surfaces and situations.
2012 was a bad, bad loss, and either signifies the end of his career or a serious injury that kept him out of the game for 7+ months--either way says nothing about his grass game specifically and more his overall health.
Same goes for Fed...the defending champion...his game has deteriorated on all surfaces, he's old! But he's still top 3 player in the world and probably best pure grass player.