In a superhero movie verse for example the recent Man of Steel wouldn’t the superhero exist in a comic book form?
Depends.
Certainly in the Marvel Universe there’s a history of superheroes having comic books published about them. Sometimes there even arises rights issues, but with secret identities who gets paid?
I don’t know about the DC universe.
Heck, in the Superman comic book universe, there was a Superman movie series starring an actor named Gregory Reed. A few stories feature Reed acting as a stand-in for Superman.
Plus there’s this cool mock movie trailer, which I cannot recommend highly enough.
The general rule* for TV or film adaptations of written works seems to be that the original work doesn’t exist in the world of the film. So, for example, in the two modernized versions of Sherlock Holmes that are currently on TV, no one has any knowledge of the Sir Authur Conan Doyle character of the same name. People in The Walking Dead don’t seem to have ever seen a zombie movie. In The Watchman comic book, comic books in the stories universe are dominated by pirate stories, since costumed crime-fighters are a real thing.
*(horror seems to be a frequent exception to this. Vampire movies, for example, often have characters who are familiar with Dracula).
Superman (and possibly the Flash) existed as a comic-book character in the Watchmen universe, though the reference was fleeting.
It makes for some interesting questions. How exactly would you write a Superman comic book, for example, in a world where Superman was a real person? You obviously can’t have any stories about him being Clark Kent because you wouldn’t know any of that. Would you just write about his public stuff as Superman? Or would you invent a secret identity for him?
Kurt Busiek dealt with some of this in his Astro City books. There was an issue about a comic book publisher who was attacked by a supervillian because he didn’t like the way the publisher portrayed him.
The Marvel universe has implied that usually, the comic stories are direct-from-the-source adaptations of “real life” adventures (most likely censored by said source where necessary for public consumption) — to the point that said comics actually have some legal weight as research. And that they too don’t like it when the publishers just make up stuff.
Very likely in a superhero universe (comic, tv, movie, video game, or other), superhero fiction would exist, but it would have a different genre landscape than in the real world.
In a universe where Superman is real, there won’t be Superman comics, unless they’re biographies or hatchet-jobs about him, but that doesn’t prevent other, purely fictional, superhero comics from having existed before… In Smallville, for instance, a superhero comic book called Warrior Angel seems to have taken the place of Superman in that universe’s fiction (there are several major parallels between Warrior Angel and Clark, some of which would be evident in-universe, others purely meta, like Fantasy Comics #1 (Warrior Angel’s first appearance) having a cover strikingly similar to Action Comics #1 (and coming out at about the same time)). Several of the main characters are fans of it - Lex, Chloe, and Oliver being the most prominent.
Captain America – in his secret identity as Steve Rogers – actually got a job for a while illustrating the Captain America comic; he got praised for drawing the fight scenes as if he’d actually been there, but he also insisted on saying the big guy should be portrayed as showing a little more introspection and doubt.
(And early on in the Fantastic Four’s run, Reed was shown visiting Stan Lee and Jack Kirby to discuss the ongoing FF comic – and shown starring in the FF movie.)
Do you remember what year that was? The City of Heroes superhero MMO had one mission where the developer of a popular MMO video game was kidnapped by members of one of the paramilitary villain organizations in the CoH world, and the authorities were speculating that they were seeking revenge because they didn’t like the way their organization was portrayed in the developer’s game.
So your character, a superhero, got sent to find and rescue the poor guy … and when you got there, the villains were just whining at the guy. While they were indeed members of the evil organization, they were also avid players of the game. They just kidnapped the guy to complain because one of them got his account banned and the other guy’s favorite character class got nerfed 
I think I might have screenshots of the conversation somewhere …
Astro City #21: “Where the Action Is” - March 2000
Cool. Then I’ll bet that scene in the game was a tribute/reference to that storyline (CoH had a lot of pop-culture references in it).
Well, in the CAPTAIN AMERICA movie – where, at one point, we see Captain America star in a Captain America movie – there is, in fact, a Captain America comic book. (And, as per THE AVENGERS, collectible Captain America trading cards.)
In the Wild Cards series, much is made of the heroes selling their rights to companies and being irritated at their portrayal.
In Superman: Secret Identity, young Clark Kent of Kansas (who never actually forgave his parent’s sense of humor for naming him ‘Clark’) was sick and tired of everyone assuming he was a Superman fan. But, the gag-gift Superman costume came in handy when his powers manifested.
He found it to be a perfect disguise, since if anyone actually got a picture of him saving an airplane or something, he knew it would be dismissed as a joke photo manipulation.
In one of the golden age Superman books, Clark Kent goes to the movies with Lois Lane. They’re playing one of the Superman cartoons. Clark has to go to various subterfuges to keep Lois from seeing his secret identity. Lois is surprised to see herself on the screen, though. Clark/Superman comments on how uncannily accurate they were about him.
In the Watchman books, the existence of superheroes means there aren’t any superhero comics; pirate comic books take their place.
Veidt sold action figures of all the Watchmen - I’d be surprised if he didn’t license comic books either. (He may have, and I just don’t remember.)
I would think comic books would exist, regardless of the fact that superheroes exist in their universe. After all, we like reading about cops, doctors, lawyers, etc – professions that do exist in our universe. Superheroes would fall into that formula for their universes.
One exception might be X-Men. Because mutants are objects of fear and revulsion, mainstream media would hold back on championing superhero mutants, which can include any sort of supernatural powers. Their superhero comics would more likely consist of ordinary Die Hard heroes saving the world from evil mutants. There would be an underground market for supernatural-based superheroes, though.
He sold actions figures of himself (and a few are on his desk when Rorschach first talks to him in his office) and was contemplating an extension of the line to include figures based on Rorschach, Nite Owl, Bubastis (Veidt’s pet lynx) and Moloch, among others, but cancelled it after defending himself from an assassination attempt. “Call the toy people and have them cancel the extension of the Ozymandias line. Tell them I don’t have enough enemies.”
This is presented in more detail in the epistolary material at the end of chapter 10, including Veidt’s note that “the public has never gone in for superheroes in a big way”. He instead proposed the villains in the Ozymandias cartoon be generic evil-organization terrorist types.
This is from memory, so my quotes might be slightly off.