"Spoken language is, in fact, no less structured and highly organised than written." MAK Halliday
It is structured and organised, but I'm not sure if it is to the same degree as written language.
He means ordinary speech, as well. He suggests that spoken English always has its own and complex grammar, quite distinct from that of written language. ;-)
Yes, it is true spoken languages very Potentials
Even in spoken language we don't use ponctuation that is considered to show "well structured" sentence but spoken language is"well structured" by the use of e.g. intonation that renders much impact to the hearer. Imagine if people miss-tune an utterance, the impact will be bigger to the hearer than miss-ponctuate to reader as found in written language. Don't forget that we do arrange primarily our utterances and fit it to such context (incl. aspect of politeness) before expressing it.
I honestly am confused by this question.