"X-Men" have long since evolved past Chris Claremont and John Byrne's contributions, "Iron Man" is decades away from it's defining Bob Layton and David Michelinie days, but they still have a presence in the market beyond their licensing appeal in other media. Contemporary fans hold out hope for the reinvigorating runs such as the Grant Morrison's take on Marvel's mutants, or even Matt Fraction's take on the armored Avenger, presented as a solid piece of well told genre entertainment. Even on titles like "Iron Fist", that had a late in the day commercial revival, its clear that the authors are mostly calling back on the original incarnation of the character, while recasting it in a more stylistically unified whole.
It's clear that the 1970s popularity of kung-fu in America that birthed the original series is decades away, but in continuing the story and adapting it to the retro sensibility of some the more accomplished modern Marvel titles, the creators at least get to indulge their own sensibilities. Yet, even when they are writing what was marketed to the fans as "the Last Iron Fist Story", and having to abandon it year and a half from the resurgence's conception, even faced with a swift cancellation following the new creative team continuing in the same vein, Marvel refuses to actually finish the story. Even at its most creative, even when there are slim chances that the character will ever garner a large following in the market place, the editorial does not accept anything but an open ending, providing for more stories down the line.
Such stubbornness is easily understandable given that the company makes most of it's sales from its ongoing titles. The older stories, even when they are much more accomplished than "Marvel Premiere" that birthed the kung fu superhero, get treated as nostalgic inspirations relevant to long time customers and discerning fans patient enough to stick with the outdated storytelling and yesterday's superhero trends. Marvel acknowledges the decades of the broad strokes of its own continuity, but theoretically, a new reader accustomed to the superhero stories needs only the working knowledge behind the character's origin and background to follow the latest renovation.
This is nowhere as clear as in Marvel's "Spider-Man", the title that has made its lead's inability to bring his often self-destructive superhero career to an end a character trait. Indeed, the publisher ultimately saw the hint of closure provided by the character's marriage and the possibility of children as working at cross purposes to the title's appeal in such a way that it went to infamously controversial stories designed with the express purpose of returning the character to his roots.
It can be said that it was Frank Miller that it was Frank Miller who was the first creator to react to this basic contradiction of the market in a creatively memorable way. By publishing his and David Mazzucchelli's "Batman: Year one", DC was well aware that it was presenting its readers with a thoughtful and stylized reconstruction of the Bob Kane originals that were seldom seen by its audience. Generally, the idea was that the character was improved upon in the years since he debuted, but placing the highly accomplished update of the character's First Act in the pages of the ongoing Batman title, it's doubtful that DC could predict how Miller would react to its eventual popularity.
Instead of producing a follow-up Year Two in the same understated retro aesthetic, to provide for an inspirational break from the continuing Second Act of Batman's regular adventures, Miller produced a much more controversial work. Taking full control of the project as the premiere writer/artist of his generation, he decided to create the final Batman story, distilling the essence of the mythos into a near-futuristic dystopia that owed as much to studio-mate Howard Chaykin as the Bob Kane (co) creations. The resulting "Dark Knight Returns" proved a landmark genre work, that worked not just as the Final Act in the Batman saga, but as a potent work in it's own right, a satire that put its creator and his artistic voice into the spotlight, at the same time both empowering the DC characters he was using, as well as transcending them.
It's all but expected, and in the history of genre fiction generally looked upon as a positive. As long as the audience responds to continuing efforts on the part of the creators and the commercial structure that supports them, the Second Act serves as a viable way to tell the story that was never truly designed with a clear endpoint in mind. Any kind of adventure storytelling basically follows this model, as long it keeps to the episodic format with little to no overall continuity.
The problems accumulated in Marvel and DC superhero universes stem from a number of inconsistencies, both in story and presentation, that stem from the continually changes in creative talent, the rigid approach to continuity and the publishers' propensity of imitating the overall trends of the moment. A much healthier model is presented in Franco-Belgian comics album tradition, where the relaxed publishing schedule and the respect of the original creator's set-up leads to a storytelling model that arguably still produces stories with no set ending, but with one clear difference.