Stability reduces potential mobility, but offloads the computation of balance, while versatility complicates everything. Limited bi-pedalism is not excluded and will be attempted. Many tradeoffs must be made to engineer a legitimate robot at this time. PA is less flexible than real humans. Each DOF is limited to 60 degrees because of engineering constraints like linearity of output.
Cylinders add their limited motions together to achieve required contortions.
The centered position all cylinders is a carefully chosen body configuration to allow the greatest kinematic script space. It resembles the dead man's float of a relaxing astronaut as identified by NASA ergometric research. The intuition here is that the greatest functionality is preserved when the centered position of all actuators corresponds to the ergometric neutral configuration. This guess, like many others, takes the place of an exhaustive and expensive inquiry for which resources are lacking. One of the author's proudest, lucky, memories is when Ralph Moser came to the first Robofest.