Remember there are a lot of "what ifs" built into the POS. The 5 day minimum is just one possibility. Restricting people to their home resort only, dropping a resort from DVC, a 5 day minimum reservation, reallocating points so every day of the year takes the same number of points...all are possible, but highly unlikely. The POS is a comprehensive legal document that tries to cover every foreseeable situation that may be encountered.
Just because they can do these things certainly doesn't mean they will do them.