"too much medium,
     not enough message"

The writing style works because those jokes, asides, and little mannerisms that are normally excluded from "serious" writing are part of how we think.

When we refine our writing (or speaking) to - supposedly to make it less jumbled and easier to read - we usually end up removing a lot of the little details that made up the original thought. The writing may have much better grammar and organization, but real thought isn't perfectly organized and we end up losing some of the "character" in the original idea. (this may be good or bad, depending on the situation)

Vi Hart has an amazing overview[1] of this concept, in which she discusses the very wise words of the Edmund Snow Carpenter in his[2] book "They Became What They Beheld".

    The trouble with knowing what to say and saying it clearly & fully, is that
    clear speaking is generally obsolete thinking. Clear statement is like an
    art object: it is the afterlife of the process which called it into being.
    The process itself is the significant step and, especially at the beginning,
    is often incomplete & uncertain.

The best way to write will always depend on what the goals are, but in general the further away from the original thought you get, the more writing and other creative ideas tend to degrade. Incidentally, this tendency of a thought to degrade the further it gets from it's origin is also how plans become policy: [3].

[1] https://www.youtube.com/watch?v=bm-Jjvqu3U4

[2] probably co-written - or at least "heavily influenced" - by Marshal McLuhan

[3] http://ogun.stanford.edu/~bnayfeh/plan.html (very mild NSFW language of the form "____ happens")