You're right, this is (unfortunately) very common. I wish there were clearer guidelines about this.

The White House Office of Management and Budget publishes IT policies, and they ask for specific URLs with www in front: https://www.whitehouse.gov/sites/default/files/omb/memoranda...

But I don't think they or anyone would care if the www redirected to the root, or vice versa, as long as it eventually got you there.