Many people have never used a CMS to manage a website and their comfort level may determine their willingness to participate in the maintenance and upkeep of the website's content through the CMS. Perhaps there are people who are really comfortable with a CMS, but their writing style doesn't carry the right tone along with the message they are trying to communicate.
In either case, there are solutions that can help you overcome these limitations. Training can be offered to users who aren't sure of how to use the system. Structures can also be setup within the CMS to ensure content is organized in an ideal manner. Approval workflows can also be implemented to ensure someone edits and approves content before its published to the site so that tone and language is consistent.