No, you can pick locks that are upside down. Ask our Euro members. They're upsidedown on just about everything.

When a lock is mounted with "key pins" down gravity will pull them downward once the pin is set, but this isn't purely necessary. If the lock is upside down, all that will happen is the key pins (often referred to as bottom pins) will rest at the shear line.
You may want to strip some pin stacks out of that lock and pick it with only 2 pins. Then work your way up to the 5 it came with.
db