There are two myths about literacy which refuse to die. The first is that writing is simply recorded speech, and the second is that since the emergence of so-called “Internet 2.0,” we are moving back to an oral culture.
I’m sorry to say that linguists are among the main propagators of that first myth. Linguists are always quick to point out that writing came along at the eleventh hour in the overall story of human language, and that any impact writing has on speech is minimal. Both of those things are true, but neither of them warrant the further assumption that writing is just a derivative of speech. If that were true, writing—particularly alphabetical writing—would be much easier to do than it is. (As I always tell my students, writing never gets easier but you do get better at it.) More to the point, as David Olson argued, writing is a model of speech which therefore involves interpretation rather than coding and decoding.