One of the reasons I've never been able to place comic book heroes in the science fiction or the fantasy genres has been common sense. Science fiction might take the idea of faster-than-light travel and run with it, but there is usually some explanation as to why they use it (Star Trek says you are traveling through subspace, Stargate has gates all over the galaxy that create artificial wormholes, Andromeda makes use of string theory and the gravity wells of stars to navigate). They might use alternate dimensions, or alternate realities, but always there is some reason.
The same goes in fantasy. There are certain types of people who can use magic, and there are always specific rules within the universe that cannot be diverted from; in Middle Earth, dwarfs cannot use Elven magic for instance. In Narnia, even Aslan cannot break the laws he has set down.
But not with comic heroes. The one that first bothered me was Superman. If comic heroes are living in the same universe we are in, but just with superheroes, then they should follow the same rules as we have to. So, when we learn that Superman's body is so dense that a single strand of his hair can lift a ton it should seem a little odd that his body is also so light that he can fly. Not jump, like the Hulk for instance, he can fly. Alien physiology or no, that just doesn't make sense in our universe.
Wonder Woman can be dead, but if you bury her in the earth she will completely heal. How? If you follow the matriarchal thinking or the New Age magic she might be reborn, but not healed.
Marvel is no better. If Spider-Man's DNA was mixed with a spider, why was his brain unaffected. It would have been a simple storyline to say he got a little dumber, but the multiple eyes and the different approach to life could have been very interesting.
Don't get me wrong, I like the heroes and I love what Marvel has been doing over the last few years, but sometimes their stuff has some serious holes in it.
So if Batman was raised during the Great Depression (1929-1939), why is he still being put in the latest cars? I wouldn't expect that of any fantasy or science fiction character. There you accept that people age and die. In the case of the distant future or a magical past they may live longer than us (the Dune universe has people's life-spans doubled by Melange), but they do age and die. Not Batman, Namor, Iron-Man, or any of the dozens of major heroes that have been around forever. Instead, comics use what's called a sliding chronology. It allows the comic companies to keep modernizing their most popular characters.
That's not science fiction or fantasy. I like the genre. I see its potential. It just frustrates me that it can't be internally consistent.
It's also frustrating when they add things, but I can live with that. When Wolverine was introduced in the 1970s he was paired with Captain America on occasion. Obviously he had never been in the World War II Captain America comics, so he had to be added retroactively. I'll not get upset with anyone for not seeing ahead 25 or 30 years. Nor will I be upset if science one day concludes that all the extra dimensions (there are probably 11 you know) are too small for interstellar travel. They could never have known that when Star Trek first came out in 1966, and though things are going that way now we still aren't sure.