It's a bit too easy and somewhat condescending to brush off public speaking as strictly inferior to written communication. In fact, I disagree strongly with Graham's stance. Sure, pure information transmission is enhanced in written form: there's less noise, the reader can skip and backtrack at will, and so on. Speaking, however, gives you many more channels, and I refuse to consider these channels (inflection, speed…
According to logocentrist theory, speech is the original signifier of meaning, and the written word is derived from the spoken word. The written word is thus a representation of the spoken word. Logocentrism asserts that language originates as a process of thought that produces speech, and it asserts that speech produces writing.