The fact that Torment had abnormal color balance took a toll on the cycles in that set.
The Tainted lands and Possessed creatures, for example, did not contain black entries because the cards were all mixtures of black with one of the other four colors. The Dreams were another story.
All the Dreams' mana costs bounced around for a while, but eventually it was decided that they would be "CC", where C stands for one colored mana. Insidious Dreams proved too good as a combo enabler at this cost, so it was bumped up to , where it remains. The other two black Dreams (black got three as opposed to one) were not powerful enough to cost , so they stayed at and , making another "imperfect" cycle.