Spoken language is backed by other optional channels of information: * Audio: speaker controls tone, speed and emphasis * Video: body language * Feedback: li

Spoken language is backed by other optional channels of information: * Audio: speaker controls tone, speed and emphasis * Video: body language * Feedback: listener can acknowledge reception or ask for repetition Written language has more time to be composed and it usually has the possibility of being ammended before submission. Therefore, I always considered natural the difference between spoken and written language styles. On a less picky opinion: agreed, complex ideas should not be written in complex language.