No, is the answer to your question. From where I'm sitting Federer's back is not to blame for everyones success in 2013.
Why not? After all, you're blaming Murray's back for Federer's relative success.
My very first post in this thread mentioned 5 set matches. Cincinnati was not a 5 set match. I'm well aware that Roger can still be a boss on the little boys circuit.
Federer outperformed Nadal at 2 of the 4 Slams. Nadal is licking his wounds and not playing the big boys' circuit.
I ignored the bit about Djokovic and Nishikori because I don't really see how it's remotely relevant. Did you watch the two matches? Kei played lights out against Novak whether he was tired or not. Stan was blowing Roger away for a set and a half, and then the rest of the match he just looked like he wanted to throw up, curl up in a ball and cry himself to sleep. Playing back to back 5 setters and then getting a 2 day rest before playing your third match is not the same as playing 3 days in a row without a break.
Considering the fragility of Nishikori, and the number of walkovers he's given in the past, two back-to-back 5-setters is a big deal. And Djokovic lost to that tired, fragile Nishikori. Federer beat tired Wawrinka. Beating a tired opponent is better than losing to a tired opponent, right?
See, I'm not exactly sure when throughout the course of the whole year where he didn't play very well this back injury was supposed to have been troubling him, but I do know that in Halle he beat 2 top 30 players en route to the title, that his loss at Wimbledon to a guy outside the top 100 was preceded by a victory over a guy inside the top 50, that before losing to Delbonis he had a couple of victories over a couple of guys inside the top 50/60, that before he lost to Rafa in Cincy (giving him as good a match as he has since probably 2011) he beat the number 13 and 29 players in the world, that he comfortably swept aside 3 guys ranked between 48 and 63 before his loss to Robredo in New York, and that between Shanghai, Basel and Bercy he accumulated 8 victories, and the lowest of those 8 opponents was ranked number 62. He had enough in the tank to play Doubles in Shanghai too.
And I'm not sure when Murray was so afflicted with injury that he couldn't even beat a 32 year-old player. Are you basing your whole, "Federer had success because of injuries," on the Australian Open alone? Why ignore his relative success at Dubai, Indian Wells, Monte Carlo, Canada, Cincinnati, and Halle? Was Murray injured at Cincinnati, too? Was Djokovic injured at Dubai?
Wait a minute... I should discredit Nadal's season because one guy was not fully healthy, because I'm discrediting Federer's season for numerous players he happened to come up against not being so? Yeah, that's the same thing.
Who are these "numerous players"? Murray and Tsonga at the Australian Open? That's one tournament, where Federer only made the semifinal. Why are you ignoring his performances at Dubai, Indian Wells, Monte Carlo, Canada, Cincinnati, Halle, Wimbledon and the US Open? If you're gonna blame all these on the health concerns of other players, then yes, Nadal's success has Federer's back to blame.