As first brought to our attention by MacRumors' Juli Clover, Apple is requiring that games created for the Apple TV must support the Apple TV remote. This means that developers cannot create games that require an external Bluetooth controller to play, although games can use Bluetooth controllers as an alternative means of control.
While this may sound a bit harsh on the part of Apple, seeing that some games feature control schemes that are more ideal for a traditional controller, I think that it's the right direction. How frustrating would it be for a user to download a game, only to find out that they can't play the game due to not having the necessary hardware? And how frustrating would it be to browse the App Store, and see tons of games that have prerequisites for a piece of hardware that didn't come bundled with the Apple TV?
This might not sit well with some developers and some gamers, but it's the right decision for the greater good.