Because we perceive print and electronic media differently. Because Marshall McLuhan was right about some things.
In case you don't recall one of the more influential thinkers of the late 20th century: McLuhan was an academic media theorist who ended up being called a "high priest of popular culture." He was big enough to be a standing joke on Laugh-In ("Marshall McLuhan, what are you doin'?") to appear in a cameo in Annie Hall, to get interviewed in Playboy. One of the fundamental things McLuhan said was that new media change us and change the world. We see that principle in every kind of technology. When films started to talk, we started to talk in their phrases and cadences. When musical notation was invented, it took music into new dimensions of complexity and length. When computers started to link up on the Internet … You get the idea.
McLuhan declared that the two epochal cultural developments of the last millennium were, first, the invention of movable type in the 15th century, which proliferated data in print and finally took humanity out of its primeval tribal culture (a culture that had already been shaken, millennia earlier, by the invention of writing). Second, the epochal change of the last two centuries was the advent of electric media, starting with the telegraph. From that point on, data started to blanket the globe at close to the speed of light.
Relatively few prophecies pan out, and plenty of McLuhan's haven't. His peaceful, neo-tribal "global village" hasn't worked so well. He predicted the end of politics, parties, and elections. Yeah, right. Still, he was the first to realize the transformation TV wrought on politics. From the pioneering Kennedy/Nixon debates to rampant political advertising and the 24-hour news cycle, TV has become the strongest force in political life. It's long been understood that a prime reason Kennedy beat Nixon for the presidency was that Kennedy looked better on TV. Now a politician's image outstrips his or her ideas—outstrips his or her politics. Which is just what McLuhan predicted: TV is about gut feeling, not reason.
One of McLuhan's central concepts is still intensely relevant in the age of Internet and e-books: his dichotomy of hot and cool media. "A hot medium," he said, "is one that extends one single sense in 'high definition.' " The less audiovisual information we have to fill in ourselves, the hotter the medium. Books and movies are "hot" because they supply a high level of information to the eye. Telephone and TV are "cool" because the telephone gives the ear "a meager amount of information," and a TV screen is less high-def than a movie. The video image, in contrast to film, is constantly being redrawn as we watch it. In the cool medium of TV, our eye and brain have to create the illusion of a complete picture; that process sucks us in, starting at the level of our synapses.
Obviously, high-definition television, which McLuhan foresaw and mused about, complicates the distinction between hot and cool media. But I'd argue that his dichotomy endures. There is a difference in how we perceive things in print and on an electronic screen. Watching TV has an innately mesmerizing effect that goes beyond whatever happens to be on. TV is addictive, druglike, in a way that movies and print aren't. Recall McLuhan's most famous aphorism: "The medium is the message." To a large extent, we respond to any medium as medium, quite apart from the content. I add that language reflects that: We "go to the movies"; we "watch TV"; we "read a book." If you're a book reader, you care more about reading itself than about any particular book.
McLuhan didn't think content was unimportant, but he believed the delivering technology is what ultimately involves and evolves us. "The 'message' of any medium or technology is the change of scale or pace or pattern that it introduces into human affairs." TV changed the world, in ways good and bad. And a computer screen is essentially a TV. Have you noticed the blank absorption on the faces of people watching TV (except, of course, for sports and politics)? It's much the same as people watching a computer screen.
(McLuhan's oracular prophecies about mass media led to his status as a pop-culture guru, which was largely a matter of misunderstanding him. TV is cool! he proclaimed. A generation grooved on that without having any idea what he meant by the word "cool." Likewise the medium is the message. Way cool! TV gets you stoned! Who cares what's on? In his Playboy interview, McLuhan, a voracious consumer of print and a lover of literature, confessed his dismay at the revolution he prophesied: "As I view the reprimitivisation of our culture … I view such upheavals with total personal dislike and dissatisfaction.")
McLuhan saw the first glimmers of the Internet and seemed to sense what was coming. He spoke of "a mosaic world in which space and time are overcome by television, jets, and computers—a simultaneous, 'all-at-once' world in which everything resonates with everything else in a total electrical field." But he may never have imagined the phenomenon of millions of people staring at a screen, not looking at TV shows but reading words on their computers, as you're doing now. That further blurs his cool-hot dichotomy. But I say again: We perceive words on-screen differently than in print. In the process of writing and teaching writing, I engage in regular experiments testing this theory.
Here's how it works, with me and with most writers I know (because I've asked). I've used computers for more than 25 years. I draft prose on-screen, work it over until I can't find much wrong with it, then double-space it and print it out. At that point I discover what's really there, which is ordinarily hazy, bloated, and boring. It looked pretty good on-screen, but it's crap. My first drafts on paper, after what amount to several drafts on computer, look like a battlefield. Here, for example, is a photo of the initial first page printout of this article.