It was clear when MI originally announced the changes. Blackout dates were gone - that is, those dates where there were no rooms available at all - and at least a limited number of rooms would be available every day of the year.
To the best of my memory, it was never presented that an unlimited number of rooms would be available. Here's what the Marriott Web Site says:
Effective January 15, 2009, hotels have standard rooms available for redemptions every day. Blackout dates traditionally refer to a limited number of dates on which a hotel could choose not to accept redemptions. With our new “No Blackout Dates” policy, hotels will no longer have blackout dates for redemptions. Hotels may limit the number of standard rooms available for redemption on a limited number of days.
(emphasis added)
I'm sorry if you confused "no more blackout dates" with "unlimited availability" but there was never a guaranty that if there was a room you would be able to use points for the room.