Writing is, indeed an essential part of Amazon's culture. I also am convinced that the writing culture contributed to the company's success. It's not just PM or SDMs. Engineers at every level are expected to write well. Most meetings often start with reading the time, even up to 30-45 mins. It does work and forces people to think as there is no difference between writing clearly and thinking clearly. I think everyone recognizes that and uses the culture to their advantage. As an SDE, I just love it.