Keep in mind what happened to get Murray to those two AO finals - Nadal was injured in their match in 2010 then faced Cilic in the semis, then Rafa had an injury-affected loss to Ferrer the round before in 2011. While it seems that Rafa and Novak get to the semis every major, at least with Rafa it's not a given in the hard court majors.
Andy's odds of getting to another final are definitely better than anyone ranked lower than him.
Why do people insist on rewriting history? Nadal was already 2 sets down when he got injured. He was on course to be straight-setted when the injury occurred.
And as far as 2011 goes, Murray has beaten Nadal at HC majors before, so it's silly to assume that Nadal's injuries are the only thing getting Murray to these finals.