Here the author seems to state that complex, multi-nested, compound or recursive statements do not arise in spoken English - obviously we must allow that the language has changed somewhat since the DoI was written - however, I know - for a fact - that I have personally uttered sentences that make the DoI's opening statement look quite concise, given my habit towards verbosity ... etc etc ad nauseam.
I apologise to anyone trying to parse the above paragraph. Spoken language does not have to worry about punctuation, spelling and can mess around with grammatical constructs. You can get away with a lot when speaking. You can use rhythm, pauses and all sorts of other tricks that are unavailable in print. You can also use facial and other gestures as well. You can fiddle with accents and other quirks as well.
That said, some written prose/documents seem to somehow transcend the limits of being pinned down on a page and take a life of their own. For example, Mr Shaksper (probably one of his famous variety of spelings) was quite handy with a pen according to a few people.