Yes, it is only for the non-
DVC options since MS would need to be able to reserve rooms at DVC resorts to "pay" for the non-DVC reservations. DVC members can always, based on availability, use DVC points for reservations at DVC resorts in the last 4 months of their Use Year. You can still use points for reservations at non-DVC options for the last 4 months - as long as those reservations were made prior to the last 4 months.
In addition, the rule-of-four also refers to the banking window where members must bank current points by the end of the 8th month.