It has nothing to do that iOS 6 can't run it is that Apple stops updating there software for devices that they don't sell anymore. They still sell the iPhone 3GS but not the iPod Touch 3rd Gen.
Is there a way to hack iOS 6 on the iPod touch 3G? One of my friends has an original iPhone with a hacked version of iOS 5.1.1 so maybe it's possible. I'm not sure.
Currently own iPod touch 3rd gen. Very happy with iOS 5. I don't think it should get iOS6, no need for it. Perfeclty works with iOS5, very smooth with minor glitches. Anyways I'm selling it very soon and getting iPod touch 5🙂