I like the idea that the Dish gave Charlie a view of Erfworld as a game as opposed to a real world, but I like to think that instead of it being a computer game that people are still playing (or the equivalent) it simply has the victory condition of only one side remaining (or whatever), at which point the game will end, or restart, or whatever. Thus conquering the world results in your own death. Basically the same as already put forward, but without there being 'players', and without Erfworld being an actual game.
And if the above is true, I wonder if, being a Carnymancer, Charlie is working towards not simply prolonging the 'game' forever, but instead working up the levels/resources to work his magic on the victory condition of Erf itself. Come to think of it, given how old he is, he must be like.... level 15+ already. I mean, Olive was 12, and she was younger than Charlie, and a few hundred turns at least have passed since then.
This would all explain alot about Charlie, but there are two things in particular that it would explain: It would explain why he opposes Stanley so much. He thinks Stanley might actually win, thus ending the world. It also explains why he is so very interested in Parson. Parson would no doubt be able to aid in the operations that Charlie is already undergoing, but would also be uniquely situated to understand what Charlie knows, and, among other things, help him in breaking that big rule.
Oh, and as someone else stated, it would show his comment about 'you can't possibly imagine what that would mean' being about Jillian being unable to understand the victory condition, as opposed to how much knowledge of his secrets getting out would hurt him.
If the above is all true, I suppose the biggest question is why Charlie doesn't tell people? Maybe just because they wouldn't believe him? They'd think he was just trying to stop wars with some made up stuff. Or maybe other Erfworlds would be literally unable to comprehend the victory condition? Or Erf starts booping him out if he tries talking about it. One of the later seems more likely, or he would have told Olive. Perhaps he was trying to use her powers to enter Stupidworld in his mind? Hell, maybe he was somehow influential in Parson's life. I kind of hope this is true, as it makes Charlie an even more awesome character than he already is.
If it was though, I wonder why he wouldn't tell Parson? Maybe from his earlier comment about people not believing info given freely? Right now though, the only way Parson is likely to believe this is if Charlie gives it as his defense when Parson has taken his City and is standing over Charlie, ready to kill him.