The fiction of audience

Writing pedagogy emphasizes the notion of audience, but John Steinbeck (via Scott Berkun) says that it (at least a general audience) doesn't exist:

Forget your general audience. In the first place, the nameless, faceless audience will scare you to death and in the second place, unlike the theater, it doesn’t exist. In writing, your audience is one single reader. I have found that sometimes it helps to pick out one person – a real person you know, or an imagined person and write to that one.