Doesn't Hilton 'force' award availability for a Diamond even if there isn't any available to others?
Not really a frorce, because there are times that a hotel can say no to the request from the Diamond desk.
The new policy doesn't affect me so much, but we often travel internationally with another couple who only gets points through their HH credit card. In the past they were able to reserve their room when we did ours,although they didn't have enough points.
By the time they would have the points I'm sure they would have had a difficult time getting their desired stay (no status).