
The problem with having a games subforum is that there aren't enough discussions that stay active to warrant having the whole attention of the main forum. Most discussions go on for about two pages and by that point every argument that can be made and every single way that you can turn it has been gone over and agreed with at least once, or people have gotten bored talking about it, and then the discussions die. The games, on the other hand, are on going threads that generally last for ages. I started the Harry Potter Point Game probably in my first month or so of being a member of this guild, and it is still on the second or first page when I am on. The discussion threads die and the games don't.
Furthermore, the main forum should have a bit of variety, I think. It's great that you want to be able to find a place to seriously discuss Harry Potter, but if a prospective member clicks on the forum and sees nothing but discussions, they may be turned off because they want to chat and have some fun with it. Subforums don't usually register with people when they're looking through a guild forum thinking about joining. On the other side of the spectrum, someone may see nothing but games and think 'oh, well, this is fun but I really want to have some good conversations' Either way, there are people who could have really enjoyed the guild who aren't going to join because they don't see the whole picture.