Apple allows only a decent set of devices to run the new firmware, including iPhone 3GS, iPhone 4, iPhone 4S, iPhone 5, iPad 2, New iPad and iPod touch 4G. Here's the complete list of features, provided by Apple, which will be and will not be available on various devices.
Quoted from iOS 6 Features Compatibility List For Supported Devices: Will Your iPhone, iPad, iPod Touch Get All The New Elements? on ipad 3 features – Yahoo! News Search Results