I think it's a case of imprecise mailing. Everyone on their list probably got the preorder email, not just the backers. It doesn't really apply to the backers unless you want more or different copies, etc.
At least, that's my guess.
If, somehow, the game comes released and I don't get a copy for my pledge... well, I'll probably just vicariously and metaphorically slaughter them through a very specific scenario and AI Plot combination.