As a reasonably intelligent reader with no axe to grind (and who, on the contrary, really enjoys reading your essays), I too was under the impression (and had no reason to question it until seeing your comment) that you were arguing that writing is an objectively better medium for conveying what I'll call ponderable information (as opposed to information that would obviously be best transmitted through spoken word, such as "get me a decaf latte with two sugars" or "there's a bear behind you") than speaking is, and that being a good writer is more important (or superior in other ways besides importance) than being a good speaker. If the latter was not your intent, please don't kill these four messengers and assume we're just bad at reading. We're simply telling you that that's how your essay comes across, at least to some readers.
This set of posts actually serves as an interesting counterargument to what I interpreted your thesis to be. As I understood it, you feel that writing gives you more time to organize your thoughts, facilitating accuracy and depth more than speaking does. Good speaking, on the other hand, or at least the kind of "good speaking" that refers to being good at captivating an audience, necessarily involves ad-libbing a lot of the details, which means you can't expect to come up with sentences that are as well worded (which usually means as precise or concise) as those you would have delivered in writing. Therefore, writing is the superior medium for delivering information. Period. Speaking is better for things like letting people see you in person (if you're famous) or sometimes better for inspiring people to take action, which you suggest are themselves important, but that speaking is inherently worse than writing for the purpose of conveying information. Am I correct so far? I apparently incorrectly extrapolated that you felt that it's intellectually superior to be a good writer than a good speaker.
Now what was I talking about this discussion serving as a counterexample to your argument? Well, first of all, I agree with everything I think you said up until the conclusion that writing is always more effective than speaking for communicating information. As we saw from this misunderstanding, the written word doesn't provide the author with the live audience feedback that the spoken word does. If multiple readers are confused, the author has no recourse because he does not know that they are confused. Thankfully they can now post comments on the Internet. :) A good speaker, on the other hand, is so in tune with his audience that he knows when they are confused or when his tone seemed misinterpreted, and he can adapt on the spot, providing more examples or changing the inflection of his voice to clarify his tone. George Carlin, one of my favorite comics, was excellent at crafting his routines, but from what I've heard from people who saw him live, was atrocious at interacting with the audience because his written style didn't allow him to deviate from his script. Nevertheless, this afforded him the planning and precision of the written word, and it worked great for him. In fields besides comedy, the written word's advantages naturally win out over the spoken word more frequently, but don't discount good speaking as an effective way to deliver information. Great speakers sometimes get an audience to understand actual content (I've seen multiple speeches were Bill Clinton did that, as well as several TED talks that did) as or more effectively than great writers do.