It is possible for this to happen in Caradorian Role-Playing, as well. With potent magics and items of immense arcane power out there in the world, your players might eventually become so potent that it becomes difficult to present viable challenges.

To help prevent this, remember these points--

First, make the acquisition of gold, power, or magic difficult. Not only will this make these acquisitions more rewarding for the players, it will also give you good ideas to base adventures around and keep the players at a potency where they still have to worry about getting into a swordfight.

Second, remember that you, as ST, wield ultimate power. Magic can wax or wane from the world, the gods can intervene and strip a vastly powerful player of his or her power (especially if they are destructive), or new and greater challenges can be created. Don't be cruel to your players -- they have worked hard to earn what they have -- but remember that mutual fun and experience is the point of role-playing -- if the player isn't having fun because nothing is challenging, and you're not having fun because the player is too powerful, introduce some loss into the game to keep things alive.