Heck, I was surprised when Coulson didn't turn up alive at the end of The Avengers
. Not only was it blatantly telegraphed by having the death off-camera, but I figured that Whedon was deliberately subverting the fans' expectations about Whedon killing off fan-favorite characters, that he was playing into that assumption in order to fake us out by having it turn out to be a ploy of Fury's.
I was wrong about the latter part (in fact, it wasn't even Whedon's idea to kill -- or "kill" -- Coulson, but came from on high), but I'm not sure it would be a retcon; again, they made a point of keeping his reputed moment of death off-camera, which is usually a dead giveaway, and these films are being made by people who seem to have a whole master strategy planned out for their productions. It's not really a retcon if they planned it that way all along; it's just a revelation of something hidden.