lil_hacker wrote: if so, would it be impossible to pick doors that have the pins on the bottom?
No.
You don't push the "lower" pins past the shear line. The spring above the "upper" pin, pushes the it right to the shear line so the lower pin wouldn't cross it.
If you do push the lower pin past the shear line the spring will either push it back past the shear line or you have to release torque and restart picking, thats the same if the lock is "pins up" or "pins down".
Matt