When Apple first announced the new streaming technology in iOS 4.2 there was a limited support when it came to what you could stream and from which apps. With the introduction of AirPlay mirroring in iOS 5 you will in the future be able to mirror pretty much everything on your iPad screen to your big screen, as long as you either have (a) an Apple TV 2 or (b) a tv with integrated AirPlay technology (sure to come soon).
The beauty of the new iPad 2 AirPlay mirroring that will come with iOS 5 when it is released later this year is that it will allow you to amongst other play your games on the big screen. What it does is basically mirror whatever is on your iPad 2 screen on to your television (given that you have the above mentioned Apple TV 2 etc.). The feature can be accessed by a control button in the multitasking tray, giving you the option to mirror when choosing AirPlay streaming.
At the moment AirPlay mirroring is only available for the iPad 2. Why it is not available for all iOS devices is unknown to us, perhaps it has to do with the iPad 2 currently being the only device with the A5 chip.