Think about this.
If you buy Sonic Generations on PC, you have to buy another copy for Nintendo3DS, XBOX360 and PS3.
Why? So Nintendo, Microsoft and SONY can profit from that instead of giving it away for free.
Like Terry, they want to profit from the game and I highly doubt that any company can give you a redeem code to download the game for free, unless Terry and companies authorize it , which I doubt it'll go through.
Either way, I'd like to see a 3DS version, but I wonder... what's the 3D going to be like? o.o