That's odd, it should work as I downloaded the game on an iPhone 3G which has iOS 4.2.1, the same as the highest possible version on the iPod Touch 2G.Ty for the reply, yes I have. I tried downloading it on an itouch 2g with 4.2(the highest possible for an itouch 2), but it asked me to upgrade to 4.3.1 without the last version compatible option.(apps like fb has offered me last version compatible option) But that isn't possible.
The 3GS goes up to iOS 6 point something I think, and the current ch just needs 4.3.1.
I'm not sure why it wouldn't allow you to download the game, perhaps try turning your device on and off again?