Along with the other things mentioned ...
Lighter overall weight of block and it lowers the weight in the car (ie lower c/g)
The shorter pushrods are then stronger/stiffer as well as lighter.
For a lower rpm engine you would probably not use a short deck block (for a sbc anyway). The very high rpm Comp type engines seem to be where these things help, especially the runner length and angle that Stan mentioned.
Rick
PS .. great site
