Do you think that's intentional?
1) a user's DropBox folder is a bit hidden away and I suspect the majority of users don't even know it's there
2) There's no reason for one user to see another user's folder if it's not to use DropBox
3) the Shared folder within Users is a bit of a permissions nightmare and requires regular 'attention' if it's actually used
Given the above, I have a CRAZY THEORY that Apple are investigating some magic, AirDrop-inspired application for the sharing of files between multiple users on the same Mac.
They got as far as hiding the display of Users and Shared, which would be redundant you've always got 'Home'.
They didn't get as far as putting the Magic New Sharing App on the updater.
And they somehow managed to put the 'hidden Users and Shared' variant up on at least one of their update distribution servers.