Not quite sure about the 'that's why its fitted with seals' is all about, no one suggested any thing would leak out just like if I stand on my head the blood does not leak out, but, I sure don't function very well.
I am assuming that the oil/fluid in the shock is below the piston and when it is compressed by hitting a lump or bump in the road the piston is forced into the oil and that oil that then passes through a venturi or hole /port or passageway to a place above the piston, and, that passing of the oil through that hole or port is what controls the speed at which the shock is compressed and as the spring returns the shock back to the decompressed state the oil is pulled back to the bottom of the shock which is the rebound.
Now I am no engineer but it would seem to me if it was upside down it would/may not function as it should.
