An example of pseudo-spoken tone from the article: "The fact that this seems worthy of comment shows how rarely people manage to write in spoken language."
That's a simple phrase to read, but I'm pretty sure it would fly right over my head if somebody dropped it in casual conversation.
I think this is an important point: most of what people verbally say is redundant noise, because in speech you have to account for people who only started really listening partway, or who need something said repeatedly in different ways to understand it. In text, the reader is free to stop and think about something, or just go back and re-read. This means that even if you're writing conversationally, it's easy and not too burdensome to compress long, rambling sentences into succinct ones that convey the same information.
That's a simple phrase to read, but I'm pretty sure it would fly right over my head if somebody dropped it in casual conversation.