I imagine it depends on what field we're talking about. I've worked in IT for a while and messages sent for company-wide purposes or to external groups are usually vetted/cleaned up by a PR group within the company. At my last job, there was an entire department titled "Strategic Communications." Basically anything the tech staff wanted to put out to the userbase had to go through SC before it could be distributed.
Again it depends on the field I guess. Technical employees write messages that other technically minded people can understand, but not your average secretary or even manager can decipher.The junior employee writes it so it can be understood and conveyed intelligently.