The Psi Disruptor, on the other hand, fit better.
-Its existence is self-explanatory. Whenever someone works on a supersoldier or a bioweapon, it always turns on them. The Confederates had watched enough action/horror movies to notice that trend, and worked on a machine to stall the Zerg if their false-flag operation went too far. Evidently, it wasn't integrated into the chain of command in time to help.

-Why we never hear about it is, well, understandable I guess. Mengsk looked for it with operatives who weren't the Magistrate/Raynor/Kerrigan, but understandably didn't have enough time to find it in the chaos.
-The UED planned to control the Zerg even before they found out about the Psi Disruptor. The Disruptor's role was to make it believable that an expeditionary force could break through the Zerg's defenses, and to depower Kerrigan. When it's destroyed, the UED still has control over the Overmind without the Disruptor, and Kerrigan has control over her broods.
-My biggest disappointment was that the Psi Disruptor is absent from StarCraft II. They could at least mention Battlecruiser-mounted units that are giving them an edge in the war against the Zerg.