I really hate that people think writing online needs to be significantly dumbed down and shorter than writing in print. Studies have shown that people are conditioned to skip around and to read only small blocks of text when reading online, but I hardly think that's the fault of the LCD they're looking at. When you compare the two mediums, print and web, I don't think the brain knows the difference between looking at letters on a computer or letters on a sheet of dead tree. LCD's do arguably cause more eye-strain, but that's slowly improving with technologies like e-ink.
The difference, I think, is our own fault. When's the last time you saw an online article that looked like page from The Hitchhiker's Guide to the Galaxy or Anathem? Don't be surprised if you can't think of one, because I can't either. Online reading is plagued by absolutely horribly designed flash ads and other sorts of chrome surrounding it. We're programmed to be drawn to motion, so if there's an invasive flash ad complete with video and animation sitting right next to a long-form article, who can blame our brain for tending to stare at it rather than focus on what we're reading?
The solution then, to online writing, is not to write ever shorter articles. Who wants to live in a world where the New York Times produces nothing but Twitter posts? Rather I think we need to bring back the long-form article and remove what has been slowly killing it: distractions, bad typography and noisy pages. Then, just maybe, we'll be able to regain the attention of the continually more distracted reader.