The funny thing is we live in an era where more people write more than ever - between Facebook, forums, online dating profiles etc. Twenty years ago the average high school graduate stopped writing anything longer than a shopping list, or maybe a letter, after age 18,
writing is another form of informal speech.
What others haven't said is that, writing is both the formulation of logical thoughts and the communication of those thoughts so they can be understood by another person. Writing and logic go hand and wrench.