I think the moratorium on house point is one of the most important details this chapter. I'd been wondering for a long time how QQ would have both Slytherin and Ravenclaw win the house cup. The points lock seems to be a way to make that happen.

The reason that's so important is that it means this is part of the plan. Harry, Draco and the rest are all in place playing their assigned roles. If they had gone off script, then they wouldn't be advancing QQ's scheme.