This mirrors many of my own thoughts. The game should be the core of the game, not people feeling their interest in the game is being lessened by not being able to post to sections of the forum. If you want to know what's happening in the south of an island, and you're in the north, pressure your ruler or ambassadors to keep you updated. Or, even better, make contact with nobles in the realms you want to know about and ask them, increasing in-game communication. Join and promote guilds or religions as mediums to hear or share more news IC.
Having a fog of war in terms of information isn't a bad thing for the game. I also think that many people who use the forums just don't realize that the majority of players in the game hardly ever (or never) visit here. Shunting more communication and interaction into the game is positive, and will help with player retention.
You're assuming that the forum is taking away from effort people would otherwise put into the game. There's no particular reason to believe that this is, in fact, the case. Nor is there any reason to believe that shutting down pieces of the forum will magically increase activity levels in the game itself.
