With iOS 4.1 coming out soon, gamers have been prepping for the launch of Game Center, an X-Box Live-like center for the unification of Apple gaming. Early versions of the 4.1 beta included Game Center support on all devices, but the newest version, 4.1 beta 3, dropped iPhone 3G Game Center support altogether. Apple states that the 3G, as well the original iPhone, are simply too slow to run the service.
I'm not exactly sure about the amount of people that are still using iDevices older than 3GS, but I assume that the number is quite large. Adding no support for older devices could be a huge blow to Apple's dreams of iDevice gaming unification, but I guess that Apple's message is clear, upgrade or be left behind.
Or who knows, maybe Apple will bring Game Center back to the older iDevices for the 4.1 launch or a later release. We'll just have to wait and see.