In 4e, if the DM wants to have a succubus have the king under her control and rule the kingdom through proxy, the DM can do so, without needing the monster’s statblock in the Monster Manual to back up that decision.
From what I can see of 4e, this is a huge shift from earlier thinking of D&D (especially 3e), where every little ability of a monster would have to be listed or it didn’t exist. The primary purpose of the 4e rules and monster descriptions is to resolve challenges (primarily combats) with the PCs. What happens with NPCs offscreen is entirely up to the DM.
Dealing with situations like “how do we break the king out of the succubus’s charm?” is in the province of the DM’s invention. This is an adventure hook, that might lead to an epic quest (“You must find the lost Mirror of Pelor and show the king the succubus’s reflection in it!”) or a simple combat (“Kill the succubus. That’ll work!”). It doesn’t need to be detailed explicitly, although pointers might be given in the abilities or descriptive text.
Why have rules, then? For those face-to-face situations where hard-and-fast rules (for combat, especially) are required. However, you only need rules for those situations, not everything that doesn’t concern the PCs… or that is part of setting up unique challenges for an adventure in any case.
At least, that’s my impression of 4e. What do you think?