P1 (think aluminum framed P38) has the safety/decocker in that orientation. Come to think of it, many S&W and Berettas have the same arrangement where parallel to the bore is fire, rotate down to decock and/or Safe. For a slide mounted safety/decocker it makes sense, but P8's decocker/safety is on the frame, which doesn't make sense.
Till the P8, Bundeswehr had the P1, not quite the longest serving side arm, think the honor goes to our beloved 1911, but still pretty long for a single stack 9mm.