The first two posts had been written (at some point I had the silly idea of doing an entire week on this topic) when another appeared that to a large degree parallels what I was writing. A writer at IO9 says that genre labels are really just reading instructions and I think he has a point. Douglas Wolk made a similar argument for comics using the inevitable though inelegant term "super-readers". Super-readers are the ones with hundreds and hundreds of comics stories in their brains, who can understand not just the character histories but the dense web of allusions, variety of techniques and good ole storytelling conventions. Super-readers are the ones who could tell you why any Spider-Man reference to a clone is meant to be funny or why the Batcave has a giant penny or could explain the rise and fall of the thought balloon.
Now the problem with comics readers is that too many prefer this so creators have taken to using super-reader familiarity as a barrier to non-comics fans instead of a shortcut or a foundation for more complex stories. (Watchmen has always reminded me of a Godard film - newcomers will get the point but the deeper your familiarity with comics and cinema the more you'll get from the work.) If you're an outsider then pick up pretty much any recent superhero comics (though this will stand out best--or is that worst?--in Blackest Night or Siege) or if you're an insider then just imagine if you didn't get any of this. Sometimes a writer will push this to the point that even super-readers balk (as Grant Morrison learned with Batman: RIP and Final Crisis) but that's pretty rare. Or sometimes a writer makes a mistake such as a recent issue of Brave and the Bold that featured Xombi, a character from a defunct company who hasn't appeared in over a decade but the writer never offered the slightest explanation of who he was.
This reading-instruction idea would also explain why so much film SF it noticably simpler (and usually simpler-minded) than written SF. Sure there's a ton of written SF that's no more thoughtful than Star Wars (not really SF but that's a topic for another time) or Avatar but the catch is that there's really not a lot of first-rate film SF and that would be because it has to be accessible for mainstream audiences. Not accessible in the sense of taking away references or ideas but in not leaving viewers feeling like they don't understand something, a feeling that SF readers take as an element of the genre. (I don't mean that SF readers believe they're too dumb to understand but that they're willing to go along with something with either the idea that the writer has figured it out or that it will be explained later, depending on how important it is to the story and maybe even the subgenre.)