Not to be that guy, but isn't the four-pack just what the price of a Steam four-pack should normally be?

$20 x 3 = $60
(Pack is 4 for the price of 3)

Edit: For example, a Borderlands 4-pack is $90, or 3 x $30).

So in other words, you're not getting a pre-order discount, exactly. If you were, the four-pack would be $54 (3 x $18), or $13.50 per unit.