Seems like instruction creep to me. Why do we need such a policy? Have there been any challenges to these principles lately? Are there likely to be?
There seems to be a desire by the board to put things in writing. There are some benefits to this. While the community knows what our values are (since they are our values), we would never do anything against this policy. However, the staff at WMF aren't necessarily members of the community with the same values we have - their job is to do what the board tells them, we can't and shouldn't assume they know what we want instinctively. These policies are how the board guides the staff.
Even if we could assume the staff are psychic, there are still problems with unwritten rules. When an unwritten rule conflicts with a written one, the written one will always take priority, regardless of which is more important. We can't really function with nothing in writing, so it's necessary to put everything in writing.