Big Head Zach
It may have to do with things like the Sentry Gun. Which could have an impact on the objectives and game if one of the sentry guns is placed in the Combat Zone.
I have a feeling that a significant percentage of people reporting that the game is too easy are probably getting this rule wrong, and putting both Sentry Guns in the Combat Zone.
Can the electric prod card move an alien from the combat area back to an empty room?
Yes, and it's essentially the card's primary purpose. It's also a great help when you're playing "A Perfect Organism" and all those double-strike aliens start flooding the complex.