The context of that win was very dodgy to say the least. Nadal had an abdominal tear - he shouldn't have been in SF in the first place, while Noserer was choking left and right, when was the last time you saw him DF in double digits and serve at ~50% in a slam? He was still owning the ballbasher even playing like shit until the choke came
Honestly, as a Fed hater, I can say that USO 2009 was the biggest waste of his career. If he didn't inexplicably choke like a mug, he would be sitting on 18 at the moment. Ferrer and many other players were never afforded an opportunity to have the stars align for them like Delpo. That's why he's a fluke. He never backed up his results, he just got hot and lucky for 2 weeks. At least Mandy made multiple slam finals until USTA gifted him the USO
Let's imagine you are right and the circumstances were really that favorable. Please tell me which players in that USO 2009 draw were of higher quality than this Nadal with an abdominal tear and 'choking' Federer. There might be a case for Djokovic, but that's pretty much it.
I agree that it was a missed chance for Federer, he had plenty of chances to win against an unexperienced opponent who, despite being on fire, was playing his first Slam final. It's still great that he didn't though, considering what happened to Del Potro after that USO - his wrist injury and surgery. Without that USO title, JMDP would be in serious jeapordy of ending his career Slamless and he's way too good a player for that. Even if injury ends up derailing the rest of his career, at least he's already got a Slam, which is only fair.
The stars can never align for Ferrer. Even if he had the nerve to win a Slam (which he doesn't), he simply doesn't have the game. Can you imagine him ever beating any of the current top 4 (and even Tsonga, Berdych...) in a Slam final?