I'm having trouble having them ring up as $9.99 in my cart. Shipping kill the deal for anyone else?
First, make sure the games you are trying to buy have the "2 for $20" in their description. The original link posted showed all games under $20, some of which are not part of the deal (Minecraft was one of the games not available in the deal).
Otherwise, as soon as you put two participating titles in your cart, their price should change to $10 a piece.
Another note, if you are trying to buy more than two, only the first two will have the reduced price. You cannot purchase more than two games per order.