Why did we use two anti-skidders instead of one? Two reasons
1) Two anti skidders far apart gives the laptop a lot of stability - both rotational and static. Obviously this can be also achieved by adding a really long anti-skidder.
2) Makes it possible to open the lid of the macbook air when it is on the stand. Notice that macbook air has a notch just infront of the trackpad, that is meant to help open the lid. If we had used only one anti-skidder, it will have to at the center and it will make this notch inaccessible.