SF in my opinion is where they imagine a certain type of technology/science and visualise it in a future setting where it is prevailent in society. An example of SF would be Steampunk. A society where everything is run by steam. This is my favourite genre in SF. But i also like Clockpunk. An example of Steampunk is Wild Wild West with Will Smith. Other examples of SF include Metropolis and maybe Astroboy. I don't understand how Star Wars is SF or Sci Fi but people just called it that.
Please elaborate on how SW isn't SF/Sci Fi, but WWW is =). In my opinion WWW is even less about technology or science than SW. The steampunk theme is just used as a gimmick, as much as the interstellar theme of SW.
On a side-note, what's your opinion on China MiƩville's steampunkish New Crobuzon novels? I absolutely love his stuff, even if it sometimes gets a bit longwinded.
'Good' SF (if there even exists such a thing as 'good' and 'bad' literature) in my opinion isn't about the future or distant worlds but explores the world the author lives in by means of imagining something 'strange' and extrapolating his/her own world using this 'strange' thing.
In that light SW and WWW both don't really fit this bill (although they can still be very good and entertaining movies!).