I understand that an exposition dump about what really happened may not have been the way to go, but I don't think retconned is the right word. Retconned implies that Brubaker deviated from his original plan, and that isn't the case. As I told the commenter below, he always planned to bring Steve back, and much more quickly than actually happened; it was only when Marvel turned the death into an event that he stretched the story out longer. That means that he always had an idea of how he'd bring him back (almost immediately, at the time) from the death, and had planted clues (like the weirdness with Steve's body's decomposition) that things weren't quite what they seemed. So from the moment Brubaker killed Steve, he knew how he'd bring him back, and this is the Vonnegut-inspired device he'd chosen for that purpose. It's fair to say it was awkwardly explained, but to say it's a retcon is like saying the reveal in Pride and Prejudice that Wickham is a bad dude was a retcon. It was always the author's plan, even if the audience and characters didn't yet know about it.

As for Tony -- yes, he's important. But so are all of the other people in Steve's life. He's not the be all and end all, and, as you said, considering what's going on in Tony's own book, it isn't really possible for him to have a present-day part in this story. (When it comes to the flashbacks, he's simply one more layer in the past Steve remembers.) But Steve WILL come back, and so will Tony (he's not going to stay lobotomized!), and they're going to reunite. Have you seen the previews for Marvel's Siege? That's going to be ALL about Steve, Tony, and Thor reuniting to take down Norman Osborn, and it'll be written by Bendis -- who, as you know, gave us The Confession. I'm not worried about Steve and Tony not getting a reunion. It's going to happen.