I think Delpo will have to wait until 2014-2016 when Djokovic and Murray will lose a step on their defense. Maybe decline will start already next year but the matchup issue against them both is too great and he seriously needs to wait for both to defend less effectively.
He can beat both of them if fit. Hell, he gave Djokovic a run for his money in New York with a bad wrist making it impossible for him to go for his BH (hence 0 BH winners), he definitely has a shot at a Slam if he can remain healthy. The two HC vs Nole this summer are hardly an indication as JMDP was playing with a bad left wrist all summer after the Olympics. He only even got to Nole because the filed below the very top lacks depth and no one could stop him despite not having a BH.
His biggest problem will remain Federer, who is a horrible matchup for him with his variety when he's playing well. Not to mention Delpo can't return Fed's serve for shit, makes Federer look like Isner on serve.