Optional peripherals are a chicken-and-egg problem.  Consumers won't buy it if there are no compelling games for it, and publishers aren't willing to commit to the peripheral (e.g., controllers not allowed) if there are not enough consumers that own the peripheral.<p>Microsoft can address this by stepping up and making Natal a required accessory for some hit game.  The trick then is finding Natal's "killer app", which we have yet to really see.<p>It's going to be tough - see Microsoft's FF Steering wheel and the 360 webcam as evidence.  The wheel is confined to racing games and isn't useful for much more, and the webcam is fun for a few nights but doesn't have a lasting appeal.  The only webcam game I'm aware of was the one shipped by MS, and it's not very fun (and very tiring on the arms).  Both devices are successful in their own scenarios, but are still niche products (how many games have you seen that use the camera?).