The tribbles now sits on an alphabetic shelf before they fall down.
This makes it easier to play, for example over the internet using Skype's new function to share your screen. Or if your opponents just are too far from the computer keyboard. Let's say you are by the keyboard, then your opponent just have to say the letter where he wants to place his tribble, then you press the letter on the keyboard and the tribble will go there. Then when everyone have placed their tribbles, the shelf is removed and the tribbles starts to fall down. (It's possible to place tribbles with the cursor keys or joystick as before too.)
The shelf also makes the game a bit more logical I think... I mean, what prevented the tribbles from starting to fall before?