It used to be fashionable as each new medium of communication appeared to proclaim that it would kill off all previous media. In particular, the democratization of video was supposed to make text obsolete. Why type “hello”, when you can make a video of yourself saying “hello”? That was the thinking, back when the videophone was The Future.
Well, video may have killed the radio star, but it certainly hasn't killed text. People, those perverse entities whose job it is to make prognosticators look foolish, have been voting with their thumbs, en masse, for text. Most of us who navigate urban sidewalks can barely pass a day without colliding with someone madly typing away on a Barbie-sized keyboard. And most of us have tales of observing two kids sitting next to each other, texting away, only to realize that they were texting to each other. People text even when it would be just as easy to communicate by voice, or for that matter video.
Has the written word killed the spoken word? Well, no, and it probably won't, at least not any time soon. There are plenty of situations where we still want to evoke of the hardwired human responses to tone of voice, or combination of voice and body language. Babies aren't going to start babbling in ASCII, and not too many people are going to buy tickets to a text-only performance of King Lear. Voice is expressive in a way that text is not.
But after 5,000 years of experience with the written word, our species has refined it to the point where text, too, is highly expressive, and what's more, expressive in a way that voice is not. Would you appreciate that cool passions of Jane Austen as much if you were listening to her sitting next to you nattering away, instead of curled up with one of her novels on a rainy afternoon? Would J.R.R. Tolkien, after his voice had given out a tenth of the way through Lord of the Rings, inspire much interest as an oral storyteller?
The written word is also powerful as much for what it does not express as for what it does. It strips away the social cues of voice, letting readers appreciate an argument undistracted by how they feel about the arguer. Text is a hierarchy-busting medium in which the mailboy's good idea can (in at least some reader's minds) outweigh the CEO's bad idea.
All the above reasons for the persistence of text in the modern world are probably familiar, but there's another one that I have not seen discussed frequently, and that is that text offers a channel for conversation that does not have to compete with the same noise (literal and figurative) as speech does. In Second Life, for example, about a third of the people I've met seem to prefer voice to text in environments where both are available, but the rest prefer text. This is not particularly surprising: many Second Life environments are devoted to music (live or recorded), and it would be rude (as well as beside the point) to talk in voice over the music. But Real Life is also full of places where it's uncomfortably loud for speech, and that probably accounts for at least some of those who text where they could talk.
The written word isn't what it used to be. Published writing used to have to pass a series of literate gatekeepers, and that's no longer the case where any idiot (like yours truly) can start a blog. Fogeys who grumble that writing is a dying art have a point, in that the quality of writing most people are likely to encounter daily has gone down over the past few decades (although there's plenty of good writing available for those who look for it). But my guess is that people today are reading and writing more words each day than ever before, even if the style is not exactly Shakespearean. The written word has served us pretty well for 5,000 years, and I expect it will be going strong 5,000 years from now, if people are still around to write.