I am curious about that same question.  All we know about Bucky's death is based purely on assumption.  Cap never saw Bucky dead and no body was ever found. All that is done here is open possibilities to new stories by reviving a character that probably didn't need to be dead to begin with.  At the same time, the writer did build a backdoor into the story should it need to be undone.

Why should Aunt May or the Human Torch be revived and Bucky stay dead?

John Byrne wrote: The death of Bucky gives birth to the "new" Captain America -- the thoughtful warrior who came out of the ice into a strange new world. It is what transforms him from a Timely character to a MARVEL character.

Interesting.  I can certainly see where you're coming from, but I'm still not clear on how Bucky's death makes Cap more thoughtful.  To me, what made him a Marvel character was the "stranger in a strange land" element, which would have happened whether Bucky died or not.  The explosion still occurs, his motivation to stop his best friend still happens, throwing Cap into the ocean to be frozen for a number of years.  He's a thoughtful warrior because of the accident that results in putting him in suspended animation and that forces him to later confront a world he doesn't know, and not as a direct result of Bucky's death.  In other words, to me, Steve Rogers is still Steve Rogers; the skinny kid who tries to enlist in WWII, is rejected and then accepts entry into a program that is supposed to create one of an army of super soldiers, only to end up being the only one due to the murder of the scientist who created the serum.  He fights for everything that America represents that is good and noble.  I'm just not sure how Bucky's death and subsequent resurrection would change any of that, unlike Uncle Ben coming back to life or Superman's parents being found to be in a state of perpetual suspended animation.

IMO Bucky's death has been used over the last few decades much the same way Jason Todd's death was used with Batman - to give the hero a good ol' dose of guilt.  That's all well and good and can serve a purpose, but I don't see it, in either case, as an indispensable part of the character.  Bucky could simply never have been mentioned again after Cap was unthawed, and IMO he'd be pretty much the same guy.

Brubaker really surpassed all my expectations with the WS arc, and I already held his work in high regard.  His Cap read to me like the "real" guy - he was thoughtful, had a very quiet strength, wasn't afraid to kick a little tail if it needed kicking, but never took that violence lightly.  IMO it's the best Cap since Gruenwald's run, and maybe since Stern/ JB.

Bucky was a symbol of the era of the Timely Captain America. His death was the catalyst that turned Timely Cap into Marvel Captain America (by giving Cap that 60's Marvel twist--guilt, tragedy, and pathos).

When Cap wakes up in Avengers # 4, he's lost everything--his partner, his life, his time. But he still manages to pick up himself up, and begins to create a new life for himself.

I don't know how much of this Stan and Jack thought out when they killed off Bucky. Most likely they just wanted to get rid of a character who was such an obvious Robin clone. Kid partners were not the thing, at Marvel. But whatever their reasons, they forged a whole new character for Captain America. One that is in no way served by a "return" of Bucky in any form.